APPLIED   ELECTROCHEMISTRY 


THE  MACMILLAN  COMPANY 

NEW  YORK  •    BOSTON  •    CHICAGO 
SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON   •    BOMBAY   •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


APPLIED 


ELECTROCHEMISTRY 


BY 


M.    DEKAY   THOMPSON,    PH.D. 
h 

ASSISTANT   PROFESSOR   OF   ELECTROCHEMISTRY   IN   THE 
MASSACHUSETTS    INSTITUTE    OF    TECHNOLOGY 


gorfc 

THE   MACMILLAN   COMPANY 
1914 

All  rights  reserved 


COPYBIGHT,   1911, 

BT  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.    Published  May,  1911.    Reprinted 
April,  1914. 


Nortooot) 

J.  8.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THE  following  book  was  written  to  supply  a  need  felt  by 
the  author  in  giving  a  course  of  lectures  on  Applied  Electro- 
chemistry in  the  Massachusetts  Institute  of  Technology.  There 
has  been  no  work  in  English  covering  this  whole  field,  and 
students  had  either  to  rely  on  notes  or  refer  to  the  sources 
from  which  this  book  is  compiled.  Neither  of  these  methods 
of  study  is  satisfactory,  for  notes  cannot  be  well  taken  in  a 
subject  where  illustrations  are  as  important  as  they  are  here ; 
and  in  going  to  the  original  sources  too  much  time  is  required 
to  sift  out  the  essential  part.  It  is  believed  that,  by  collecting 
in  a  single  volume  the  material  that  would  be  comprised  in 
a  course  aiming  to  give  an  account  of  the  most  important  elec- 
trochemical industries,  as  well  as  the  principal  applications  of 
electrochemistry  in  the  laboratory,  it  will  be  possible  to  teach 
the  subject  much  more  satisfactorily. 

The  plan  adopted  in  this  book  has  been  to  discuss  each 
subject  from  the  theoretical  and  from  the  technical  point  of 
view  separately.  In  the  theoretical  part  a  knowledge  of  theo- 
retical chemistry  is  assumed. 

Full  references  to  the  original  sources  have  been  made,  so 
that  every  statement  can  be  easily  verified.  It  is  thought  that 
this  will  make  this  volume  useful  also  as  a  reference  book. 

An  appendix  has  been  added,  containing  the  more  important 
constants  that  are  needed  in  electrochemical  calculations. 

Thanks  are  due  to  the  following  individuals  and  companies 
for  permission  to  reproduce  cuts,  or  to  use  the  material  in  the 
text,  or  for  both:  the  American  Academy  of  Arts  and  Sci- 
ences ;  the  American  Electrochemical  Society ;  the  Carborun- 
dum Company ;  Wilhelm  Engelmann ;  Ferdinand  Enke ;  the 
Electric  Storage  Battery  Company;  the  Engineering  and 
Mining  Journal;  the  Faraday  Society;  the  Franklin  Insti- 


387459 


VI  PREFACE 

tute ;  Charles  Griffin  and  Company ;  Gould  Storage  Battery 
Company ;  Dr.  Eugene  Haanel ;  the  Hanson  and  Van  Winkle 
Company;  Mr.  Carl  Hering;  Mr.  Walter  E.  Holland  of 
Thomas  A.  Edison's  Laboratory ;  International  Acheson 
Graphite  Company;  Wilhelm  Knapp;  Longmans,  Green  and 
Company ;  Progressive  Age  Publishing  Company ;  Dr.  E.  F. 
Koeber,  Editor  of  the  Metallurgical  and  Chemical  Engineer- 
ing;  Julius  Springer;  Spon  and  Chamberlain;  John  Wiley 
and  Sons. 


TABLE   OF   CONTENTS 

CHAPTER  I 

PAGES 
COULOMETERS    OR    VOLTAMETERS 1-12 

1.  General  Discussion  —  2.  The  Silver  Goniometer  —  3.  The 
Copper  Goniometer  —  4.  The  Water  Goniometer  —  5.  The  Silver 
Titration  Goniometer. 

CHAPTER  IT 

ELECTROCHEMICAL  ANALYSIS 13-29 

1.   Nonelectrolytic  Methods  —  2.   Electrolytic  Methods. 

CHAPTER  III 

ELECTROPLATING,  ELECTROTYPING,  AND  THE  PRODUCTION  OF  ME- 
TALLIC OBJECTS 30-42 

1.  Electroplating:  Nickel  Plating ;  Copper  Plating ;  Zinc  Plat- 
ing ;  Brass  Plating ;  Silver  Plating ;  Gold  Plating  —  2.  Gal- 
vanoplasty :  Electrotyping ;  Copper  Tubes,  Foil,  and  Wire. 

CHAPTER  IY 

ELECTROLYTIC  WINNING  AND  REFINING  OF   METALS  IN  AQUEOUS 

SOLUTIONS 43-67 

1.  The  Winning  of  Metals:  Copper  and  Zinc— 2.  The  Elec- 
trolytic Refining  of  Metals:  Copper  Refining;  Nickel  Refining; 
Silver  Refining  ;  Gold  Refining  ;  Lead  Refining ;  Zinc  Refining. 

CHAPTER  V 

ELECTROLYTIC  REDUCTION  AND  OXIDATION         ....        68-79 
1.   Reduction  —  2.   Oxidation. 

CHAPTER  VI 

ELECTROLYSIS  OF  ALKALI  CHLORIDES 80-136 

1.  Theoretical  Discussion  :  The  Chemical  Action  of  Chlorine  on 
Water  and  Alkali  Hydrate;  The  Electrolysis  of  Alkali  Chloride  on 

vii 


TABLE    OF   CONTENTS 

PAGES 

Smooth  Platinum  Electrodes  without  a  Diaphragm;  The  Electrolysis 
of  Alkali  Chlorides  with  Platinized  Platinum  Anodes;  The  Electrol- 
ysis of  Alkali  Chlorides  on  Carbon  Anodes;  The  Maximum  Concen- 
trations of  Hypochlorite  and  the  Maximum  Current  and  Energy  Yields 
of  Hypochlorite  and  Chlorate;  The  Production  of  Perchlorates ;  The 
Electrolysis  of  Alkali  Chlorides  with  a  Diaphragm;  Decomposition 
Points  and  Potentials  of  Alkali  Chloride  Solutions;  Fluorides, 
Bromides,  and  Iodides  —  2.  Technical  Cells  for  Hypochlorite, 
Chlorate,  Hydrate,  and  Chlorine. 


CHAPTER  VH 
THE  ELECTROLYSIS  OF  WATER 137-141 

CHAPTER  VHI 
PRIMARY  CELLS       . 142-151 

CHAPTER  IX 

THE  LEAD  STORAGE  BATTERY 152-172 

1.  History  and  Construction  —  2.  Theory  of  the  Lead  Storage 
Battery. 

CHAPTER  X 

THE  EDISON  STORAGE  BATTERY 173-184 

1.  General  Discussion  —  2.  Theory  of  the  Edison  Storage 
Battery. 

CHAPTER  XI 

THE  ELECTRIC  FURNACE 185-201 

1.   General  Discussion  —  2.  Electric  Furnace  Design. 

CHAPTER  XII 

PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE  .        .        .    202-238 

1.  Calcium  Carbide  —  2.  Carborundum  —  3.  Siloxicon— 4.  Sili- 
con—  5.  Graphite  — 6.  Carbon  Bisulphide  —  7.  Phosphorus  — 
8.  Alundum  —  9.  Aluminum  —  10.  Sodium  and  Potassium  — 
11.  Calcium. 


TABLE    OF   CONTENTS  IX 

CHAPTER   XIII 

PAGES 

THE  ELECTROMETALLURGY  OF  IRON  AND  STEEL         .        .        .    239-264 

1.  General  Discussion  —  2.  The  Electrothermic  Reduction  of 
Iron  Ores  —  3.  The  Electrothermic  Refining  of  Steel. 

CHAPTER  XIV 

THE  FIXATION  OF  ATMOSPHERIC  NITROGEN        ....    265-287 

1.  Introduction  —  2.  Absorption  by  Calcium  Carbide  —  3.  The 
Oxidation  of  Nitrogen  —  4.  The  Synthesis  of  Ammonia  —  5.  Con- 
clusion. 

CHAPTER  XV 

THE  PRODUCTION  OF  OZONE 288-314 

1.  General  Discussion :  The  Maximum  Concentration;  Yield  per 
Coulomb  for  Negative  Point  Electrode ;  Yield  per  Coulomb  for  Posi- 
tive Point  Electrode ;  Yield  per  Kilowatt  Hour  for  Positive  and  for 
Negative  Points;  Theory  of  Ozone  Formation  by  Silent  Discharge; 
The  Siemens  Ozonizer  —  2.  The  Technical  Production  of  Ozone. 

APPENDIX 315-321 

Atomic  Weights  —  Electrochemical  Equivalents  —  Numerical 
Relation  between  Various  Units  —  Legal  Electrical  Units. 

NAME  INDEX 323-325 

SUBJECT  INDEX 327-329 


LIST   OF  ABBREVIATIONS 

Ann.  d.  Phys Annalen  der  Physik. 

Ann.  d.  Chem.  und  Pharm.  .     .  Annalen  der  Chemie  und  Pharmacie. 

Ann.  d.  Chim.  et  de  Physique  .  Annales  de  Chimie  et  de  Physique. 

B.  B Berichte  der  Deutschen  Chemischen  Gesell- 

schaft. 
Berg-  und  Hiittenm.  Ztg.      .     .     Berg-  und  Hiittenmanische  Zeitung. 

Chem.  News Chemical  News. 

Chem.  Zeitung Chemiker  Zeitung. 

C.  R Comptes  Rendus  des  Seances  de  1'Academie 

des  Sciences. 

Dingler's  polyt.  J Dingler's  Polytechnisches  Journal. 

Electrochem.  and  Met.  Ind.       .     Electrochemical     and     Metallurgical    In- 
dustry. 

Electroch.  Ind. Electrochemical  Industry. 

Elektrotech.  Z Elektrotechnische  Zeitschrift. 

El.  World Electrical  World. 

Eng.  and  Min.  J Engineering  and  Mining  Journal. 

Gilbert's  Ann Gilbert's  Annalen. 

J.  f.  prakt.  Ch Journal  fur  praktische  Chemie. 

Journ.  of  the  Franklin  Inst.      .     Journal  of  the  Franklin  Institute. 

J.  Am.  Chem.  Soc Journal  of  the  American  Chemical  Society. 

Met.  and  Chem.  Eng Metallurgical  and  Chemical  Engineering. 

Min.  Ind Mineral  Industry. 

Phil.  Mag Philosophical  Magazine. 

Phil.  Trans Philosophical  Transactions. 

Phys.  Rev Physical  Review. 

Pogg.  Ann Poggendorff's  Annalen. 

Proc.  Am.  Acad Proceedings  of  the  American  Academy  of 

Arts  and  Sciences. 

Proc.  Am.  Phil.  Soc.     ....     Proceedings    American   Philosophical   So- 
ciety. 

Proc.  Royal  Soc.  of  Edinburgh     Proceedings  of  the  Royal  Society  of  Edin. 

burgh. 

Proc.  Soc.  Arts Proceedings  of  the  Society  of  Arts,  Boston. 

Trans.  Am.  Electrochem.  Soc.  .     Transactions  of  American  Electrochemical 

Society. 

Z.  f.  anal.  Ch Zeitschrift  fur  analytische  Chemie. 

xi 


Xii  LIST    OF   ABBREVIATIONS 

Z.  f.  angew.  Ch Zeitschrift  fiir  angewandte  Chemie. 

Z.  f.  anorg.  Ch Zeitschrift  fiir  anorganische  Cheraie. 

Z.  f.  Berg-,  Hiittenm.-  und  Salinen-Wesen.     Zeitschrift  fiir  das  Berg-,  Hut- 

tenmanische-     und     Salinen-Wesen     in 

preussische  Staaten. 

Z.  f.  Elektroch Zeitschrift  fiir  Elektrochemie. 

Z.  f.  phys.  Ch Zeitschrift  fiir  physikalische  Chemie. 


APPLIED   ELECTROCHEMISTRY 


APPLIED  ELECTROCHEMISTRY 

CHAPTER  I 

X 

COULOMETERS1  OR  VOLTAMETERS 
1.    GENERAL  DISCUSSION 

AN  important  application  of  electrolysis  is  the  determination 
of  the  amount  of  electricity  passing  through  a  circuit  in  a  given 
time.  According  to  Faraday's  laws,  (1)  the  magnitude  of  the 
chemical  effects  produced  in  a  circuit  is  proportional  to  the 
quantity  of  electricity  that  passes  through  the  circuit,  and  (2) 
the  quantities  of  the  different  substances  which  separate  at 
electrodes  throughout  the  circuit  are  directly  proportional  to 
their  equivalent  weights.2  The  first  statement  is  true  under  all 
conditions,  but  the  second  only  for  the  case  that  a  single  sub- 
stance is  liberated  on  any  given  electrode.  If  several  sub- 
stances are  deposited  together  on  the  same  electrode,  there  is, 
of  course,  less  of  each  than  if  only  one  is  deposited. 

The  electrochemical  constant,  or  the  quantity  of  electricity 
necessary  to  deposit  one  equivalent  weight  of  any  substance, 
has  been  accurately  determined  by  measuring  the  amount  of 
silver  deposited  for  a  known  quantity  of  electricity.  The 
value  of  this  constant  generally  accepted  is  96,540  coulombs, 
and  is  accurate  to  a  few  hundredths  of  a  per  cent.3 

1  This  name  was  proposed  by  T.  W.  Richards,  Proc.  Am.  Acad.  37, 415,  (1902). 

2  Le  Blanc,  Electrochemistry,  English  translation,  p.  42,  (1907). 

3  Nernst,  Theoretische  Chemie,  6th  ed.,  p.  716,  (1909)  ;  Guthe,  Bulletin  of  the 
Bureau  of  Standards,  1,  362,  (1905). 

B  1 


2-- 


'     •  • 

"*  ALLIED.. ELECTROCHEMISTRY 


It  is  evident  from  the  above  that  the  amount  of  electricity 
passing  through  a  circuit  can  be  determined  from  the  amount 
of  chemical  change  produced  at  any  electrode  if  this  chemical 
change  can  be  measured.  There  are  three  general  methods  of 
making  this  measurement :  (1)  by  weighing  the  substance  de- 
posited or  liberated,  (2)  by  measuring  its  volume,  and  (3)  by 
titration.  It  seems  hardly  necessary  to  call  attention  to  the 
fact  that  in  any  coulometer  the  current  can  be  computed  from 
the  quantity  of  electricity  that  has  passed  through  the  circuit, 
if  the  current  has  been  constant  and  if  the  time  is  measured. 
Current  in  amperes  equals  quantity  in  coulombs  divided  by 
time  in  seconds. 

The  errors  of  coulometers  are  those  inherent  in  the  measure- 
ment of  weight  and  volume  or  in  titration,  and  also  those  due 
to  imperfections  in  the  coulometer  itself.  The  latter  may 
come  from  a  variety  of  causes,  such  as  the  liberation  of  other 
substances  than  the  one  assumed,  or  the  loss  of  the  substance 
after  deposition  and  before  weighing.  The  errors  of  each 
coulometer  described  below  will  be  pointed  out. 

2.  THE  SILVER  COULOMETER 

The  silver  coulometer  is  the  most  accurate  of  all  electro- 
chemical coulometers.  It  is  for  this  reason  that  it  is  used  to 
determine  the  electrochemical  constant.  It  consists  of  a  plati- 
num dish  cathode,  a  neutral  silver  nitrate  solution  made  by 
dissolving  20  to  40  grams  of  nitrate  in  100  grams  of  distilled 
water,  and  a  pure  silver  anode.  By  weighing  the  platinum 
dish  before  and  after  the  current  has  passed,  the  amount  of 
electricity  may  be  computed  from  the  value  of  the  electro- 
chemical equivalent  of  silver  given  above.  To  obtain  the  best 
results,  the  anode  should  be  wrapped  in  filter  paper,1  in  order  to 
prevent  any  silver  mechanically  detached  from  the  anode  from 
falling  into  the  platinum  dish,  or  contained  in  a  porous  cup, 
which  also  separates  the  anode  solution  from  the  cathode.  The 
solution  from  the  anode  would  deposit  too  much  silver  on  the 

1  Richards,  Collins,  and  Heimrod,  Proc.  Am.  Acad.  35,  143,  (1899). 


COULOMETERS  OR  VOLTAMETERS 


cathode,  due  to  the  formation  of  a  complex  silver  ion,  prob- 
ably Ag+,  which  does  not  break  up  at  once  to  the  normal  ion 
Ag+  and  2  Ag,  and  which,  if  deposited,  would  give  too  great  a 
quantity  of  silver.2  This  is  the  main  source  of  error,  and  when 
it  is  excluded,  the  mean  error  of  one  determination  is  about 
0.03  per  cent,  for  a  deposit 
weighing  not  less  than 
half  a  gram.3  The  cou- 
lometer  used  by  Richards, 
Collins,  and  Heimrod  is 
shown  in  Figure  1. 

The  solution  of  silver 
nitrate  may  be  used  until 
a  deposit  corresponding  to 
3  grams  of  silver  from  100 
cubic  centimeters  of  solu- 
tion has  been  reached. 
The  current  density  must 
not  exceed  0.2  ampere  per 
square  centimeter  on  the 
anode,  or  0.02  ampere  per 
square  centimeter  on  the 
cathode.  The  silver  ni- 
trate solution  must  be 
thoroughly  washed  out 
before  weighing,  until  the 
wash  water  gives  no  test 
for  silver  with  hydro- 
chloric acid.  The  dish  is 
then  dried  and  weighed. 

The  silver  deposit  from 
the  nitrate  solution  is  crystalline,  and  does  not  form  a  smooth 
coating,  and  for  this  reason  there  is  danger  of  losing  some  of 
the  crystals  in  washing.  Silver  can  be  deposited  with  a  smooth 
surface  from  the  double  cyanide  of  silver  and  potassium,  and  it 

2 Richards  and  Heimrod,  Proc.  Am.  Acad.  37,  415,  (1902). 

3  Ostwald-Luther,  Hand-  und  Hiilfsbuch,  3d  ed.  p.  497,  (1910). 


FIG.  1.  —  Porous  cup  coulometer  (§  actual  size) 

A,  glass  hook  for  supporting  anode.  £,  glass  ring  for 
supporting  porous  cup.  O,  silver  anode.  D,  porous 
cup.  E,  platinum  cathode. 


APPLIED   ELECTROCHEMISTRY 


has  been  found  that  a  coulometer  using  this  liquid,  on  exclud- 
ing oxygen,  gives  accurate  results  without  the  danger  of  de- 
taching any  silver  in  weighing.4 


3.    THE  COPPER  COULOMETER 

The  copper  coulometer  consists  usually  of  two  sheets  of 
copper  for  anodes,  with  a  thin  copper  sheet  hung  between 
them  as  cathode,  in  an  acid  solution  of  copper  sulphate.  It 
is  not  so  accurate  as  the  silver  coulometer  for  several  reasons. 
In  the  first  place,  only  0.29  gram  copper  is  deposited  to  every 
gram  of  silver.  This  reduces  the  percentage  accuracy  of  the 
weight  to  about  one  third  of  the  value  it  would  have  for  an 
equivalent  amount  of  silver.  More  important  than  this  are 
the  chemical  reactions  that  tend  to  change  the  weight  of 
copper  deposited  on  the  cathode  from  the  correct  weight. 
The  copper  cathode  dissolves  slightly  in  acid  cupric  sulphate, 
forming  cuprous  sulphate : 

Cu  +  Cu++  =  2  Cu+, 

thereby  reducing  the  weight  of  the  cathode.  This  takes  place 
to  a  less  extent  if  oxygen  is  excluded.  On  the  other  hand,  in 
a  neutral  solution  the  plate  gains  in  weight,  due  to  a  covering 
of  cuprous  oxide  coming  from  hydrolysis  of  the  cuprous 
sulphate.  With  increasing  temperature  not  only  does  the 
velocity  of  the  above  reaction  increase,  but  also  the  amount 
of  cuprous  ions  in  equilibrium  with  cupric  ions,  and  conse- 
quently more  cuprous  ions  are  deposited.  Wherever  cuprous 
ions  are  deposited,  the  weight  of  copper  is  too  great,  as  the 
electrochemical  equivalent  of  cuprous  copper  is  double  that  of 
cupric. 

The  solution  generally  used  in  the  copper  coulometer  is  that 
recommended  by  Oettel,1  consisting  of  1000  grams  of  water, 
150  grams  of  crystallized  copper  sulphate,  50  grams  of  concen- 

*  Farup,  Z.  f.  Elektroch.  8,  669,  (1902). 
1  Chem.  Zeitung,  17,  643,  and  677. 


COULOMETERS   OR   VOLTAMETERS 


FIG.  2.  —  Copper  coulometer 


6  APPLIED    ELECTROCHEMISTRY 

trated  sulphuric  acid,  and  50  grams  of  alcohol.  The  alcohol 
drives  back  the  dissociation  of  the  cupric  sulphate,  reducing 
the  concentration  of  the  cupric  ions  and  therefore  of  the  cu- 
prous ions  in  equilibrium  with  them.2  For  ordinary  purposes 
the  exclusion  of  air  is  not  necessary.  The  current  density  on 
the  cathode  should  lie  between  2  and  20  milliamperes  per 
square  centimeter.  The  advantages  of  the  copper  over  the 
silver  coulometer  are  its  greater  cheapness  and  the  greater 
adhesiveness  of  the  deposit  on  the  cathode.  The  average  error 
of  a  single  determination  is  from  0.1  to  0.3  per  cent.3  A 
convenient  form  of  the  copper  coulometer  is  shown  in  Fig- 
ure 2.  The  inside  dimensions  of  the  glass  vessel  are  approxi- 
mately 4.3  centimeters  in  width,  16  centimeters  in  height, 
and  17  centimeters  in  length. 

4.   THE  WATER  COULOMETER 

The  water  coulometer  measures  the  quantity  of  electricity 
passing  through  a  circuit  by  the  amount  of  water  decomposed 
between  unattackable  electrodes  dipping  in  a  solution  through 
which  the  current  flows.  The  amount  of  water  decomposed 
may  be  determined  by  measuring  the  loss  in  weight  of  the 
coulometer,  by  measuring  the  total  volume  of  gas  produced, 
or  by  measuring  the  volume  of  either  one  of  the  gases 
separately. 

The  decomposition  of  water  by  the  electric  current  was  first 
observed  by  Nicholson  and  Carlisle l  in  1800.  In  1854  Bunsen2 
used  a  water  coulometer  in  which  the  loss  in  weight  was  deter- 
mined ;  and  since  then  others  have  devised  coulometers  on  the 
same  principle.3  Figure  3  shows  a  convenient  form  of  the 
apparatus,  having  a  drying  tube  sealed  directly  to  it ;  for  be- 
fore leaving  the  cell  the  gases  must,  of  course,  be  thoroughly 

2  Foerster  and  Seidel,  Z.  f.  anorg.  Ch.  14,  135,  (1807). 

8  Ostwald-Luther,  Hand-  und  Hiilfsbuch,  3d  ed.  497,  (1910). 

1  Gilbert's  Ann.  6,  340,  (1800). 

2  Pogg.  Ann.  91,  620,  (1854). 

8  L.  N.  Ledingham,  Chein.  News,  49,  85,  (1884). 


COULOMETEKS  OR  VOLTAMETERS 


Glass  wool 


Sealed  joint 


dried  so  that  no  water  vapor  is  carried  off  with  them.  It  is 
evident  that  this  instrument  cannot  give  great  accuracy  on 
account  of  the  relatively  small  change 
in  weight  produced  by  the  passage 
of  an  amount  of  electricity  equal  to 
the  electrochemical  constant.  In 
the  case  of  water  the  change  in 
weight  is  only  9  grams,  as  com- 
pared with  31.2  grams  of  copper 
and  107.9  grams  of  silver.  The 
errors  inherent  in  the  instrument 
itself  are  due  to  the  formation  of 
other  products  than  hydrogen  and 
oxygen.  If  a  solution  of  sulphuric 
acid  is  used  between  platinum  elec- 
trodes, the  oxygen  liberated  on  the 
anode  contains  a  certain  amount  of 
ozone.4  Persulphuric  acid,  H2S2O8, 
and  hydrogen  peroxide,  due  to  the 
oxidation  of  water  by  the  persul- 
phuric  acid,  are  also  produced.  The 
production  of  persulphuric  acid  is  a 
maximum  when  the  concentration  of 
the  solution  is  between  30  and  50 
grams  of  sulphuric  acid  to  100 
grams  of  water.5  For  this  reason  a 
10  to  20  per  cent  solution  of  sodium 
hydrate  is  often  used,  in  which  none 
of  the  above  disturbing  reactions 
occur. 

The    presence    of    even    a    small 

amount  of  salt  of  a  metal  with  two  different  valences,  such  as 
iron,  may  cause  a  very  large  error.  Table  1  shows  what  the 
magnitude  of  this  error  is  for  iron  impurities.6 

4  Schonbein,  Pogg.  Ann.  50,  616,  (1840). 

6  Franz  Richarz,  Ann.  d.  Phys.  24,  183,  (18oo);  31,  912,  (1887). 

e  Elbs,  Z.  f.  Elektroch.  7,  261  (1900). 


FIG.  3.  —  Water  coulometer 


8 


APPLIED   ELECTROCHEMISTRY 
TABLE  1 


IRON  CONTENT  IN 
PER  CENT 

CURRENT  DENSITY  PER 
SQUARE  DM. 

Loss  IN  DETONATING  GAS 
IN  PER  CENT 

1.0 

2.23 

48.3 

1.0 

0.228 

97.4 

0.1 

6.4 

3.0 

0.1 

0.35 

25.1 

0.01 

2.22 

1.7 

0.360 

6.3 

It  is  to  be  noticed  that  this  error  is  diminished  by  increasing 

the  current  density. 

Sulphuric  acid  of  1.14  specific  gravity  has  been  shown  by 

F.  Kohlrausch7  to  give  results 
as  accurate  as  the  measurements 
themselves  in  coulometers 
where  the  total  volume  of  gas 
is  measured.  He  simultane- 
ously devised  a  form  of  coulom- 
eter  shown  in  Figure  4.  The 
glass  tube  is  4  centimeters  in 
diameter  and  is  divided  into 
units  of  5  cubic  centimeters. 
The  base  contains  500  cubic 
centimeters.  The  anode  is 
platinum  foil,  4  centimeters 
long  and  1.7  centimeters  wide, 
placed  between  two  cathodes  of 
the  same  size.  To  refill  the 
tube  it  is  simply  turned  upside 
down.  A  thermometer  is  sealed 
in  for  determining  the  tempera- 
ture of  the  gas.  On  account  of 
the  limited  volume  of  this  ap- 

FIO.  4. — Kohlrausch  water  couiometer     paratus,  large  quantities  of  elec- 

7  Elektrotech.  Z.  6,  190,  (1885). 


COULOMETERS  OR  VOLTAMETERS 


9 


tricity  cannot  be  measured;  it  is  intended  for  the  measurement 
of  currents  between  3  and  30  amperes.  The  relation  between 
the  volume  of  gas  generated  in  one  second,  saturated  with 
water  vapor  at  the  vapor  pressure  corresponding  to  a  sulphuric 
acid  solution  of  specific  gravity  1.14,  and  the  current  is  as 
follows:  For  20°  and  a  pressure  of  72.5  centimeters  of  mercury, 
one  ampere  in  one  second  produces  0.2  cubic  centimeter  of  gas, 
including  the  water  vapor.  Therefore,  under  these  conditions 
of  temperature  and  pressure,  the  number  of  cubic  centimeters 
of  gas  generated  per  second,  when  multiplied  by  5,  gives  the 
current  in  amperes.  The  corrections  for  the  volume  in  thou- 
sandths of  a  cubic  centimeter  for  different  temperatures  and 
pressure  are  given  in  Table  2. 

TABLE  2 

Corrections,  in  Thousandths  of  a  Cubic  Centimeter,  for  Reducing  the  Volume  of  Gas 
generated  in  One  Second  to  the  Value  which,  multiplied  hy  5,  gives  the  Current. 
Specific  Gravity  of  Sulphuric  Acid  :  1.14 


TEMP.  CENTIGRADE 
DEGREES 

700 

mm. 

710 

mm. 

720 

mm. 

730 

mm. 

740 

mm. 

750 

mm. 

760 

mm. 

10 

9 

24 

38 

53 

68 

82 

97 

11 

5 

19 

33 

48 

63 

78 

93 

12 

1 

15 

29 

44 

59 

73 

88 

13 

-4 

10 

24 

39 

54 

69 

83 

14 

-8 

6 

20 

35 

49 

64 

78 

15 

-13 

2 

16 

30 

44 

59 

73 

16 

-17 

-3 

11 

26 

40 

54 

68 

17 

-22 

—  7 

7 

21 

35 

49 

63 

18 

-26 

-12 

2 

16 

30 

45 

59 

19 

-31 

-17 

-3 

11 

26 

40 

54 

20 

-35 

-21 

-7 

7 

21 

35 

49 

21 

-40 

-26 

-12 

2 

16 

30 

44 

22 

-44 

-30 

-17 

-3 

11 

25 

39 

23 

-49 

-35 

-22 

-8 

6 

20 

34 

24 

-54 

-40 

-26 

-12 

1 

15 

29 

25 

-58 

-45 

-31 

-17 

-4 

10 

24 

10 


APPLIED   ELECTROCHEMISTRY 


The  following  example  will  illustrate  the  use  of  this  table. 

Barometer,  0° 754  millimeters  of  mercury. 

Height  of  sulphuric  acid  in  tube     112  millimeters  of  mercury. 
Pressure  in  gas  =  754  -  -^  =  745. 
Temperature  of  gas  :  17. °8. 

Volume  of  gas 198.0  cubic  centimeters. 

Correction  :      +  0.038  x  198.0  =          7.5  cubic  centimeters. 

205.5  cubic  centimeters. 
Duration  of  experiment :  39  seconds. 
Therefore  in  one  second  5.27  c.c.  of  gas  were  generated. 
Current  =  5.27  x  5  =  26.3  amperes. 

>    k  ._.  On  comparison  with  a  tangent  galvanom- 

X^A  eter  the  current  indicated 

YJU  by    this    coulometer    was 

found  on  an  average  to  be 

\  per  cent  low. 

In  order  to  avoid  correc- 
tion for  the  height  of  the 

solution,    the    instrument 

may  be  made  like  a  Hem- 
pel  gas  analysis  burette,  as 

shown  in  Figure  5. 

A  very  convenient  form 

of   water    coulometer   has 

been  devised  by  F.  C.  G. 

Miiller,8  shown  in  Figure 

6.     The  whole   apparatus 

is  placed  in  a  water  bath, 

so  that  the  temperature  of 

the  gas  can  be  determined. 

A  is  the  electrolytic  cell 

filled  with  barium  hydrate, 

which  does  not  foam  like 

sodium  or  potassium  hy- 
drate. 


Fio.  5. —  Water  cou- 
lometer 


ceiver. 


F  is   the   gas   re-      ~~ 

mi          ,,  FiG.6.  — Miiller's  water 

The     three-way  coulometer 


8  Z.  f.  d.  phys.  und  chem.  Unterricht,  14,  140,  (1901). 


COULOMETERS  OR  VOLTAMETERS  11 

stopcock  at  the  top  allows  the  gas  to  escape  through  H  when 
no  measurement  is  to  be  made.  By  turning  the  stopcock  at  a 
given  second,  the  gas  passes  into  H,  which  is  previously  filled 
with  water  to  the  upper  mark.  When  H  is  filled  with  gas, 
the  stopcock  is  turned  to  allow  the  gas  to  pass  out  H  and  the 
time  noted.  This  apparatus  can  thus  be  left  connected  in  the 
circuit  and  a  measurement  made  at  any  time. 

The  water  coulometer  may  be  transformed  into  a  direct  read- 
ing ammeter  by  a  method  first  applied  in  1868  by  F.  Guthrie.9 
If  the  gas  is  allowed  to  escape  through  a  small  hole,  a  definite 
pressure  in  the  instrument  is  developed,  depending  on  the  cur- 
rent and  size  of  the  hole.  The  pressure  is  measured  by  a 
mercury  or  water  manometer.  This  same  principle  has  been 
rediscovered  by  J.  Joly,10  Bredig  and  Hahn,11  and  Job.12  In 
Bredig  and  Hahn's  apparatus  the  gas  escapes  through  capillary 
tubes,  and  by  using  a  tube  with  different  bores  the  range  of 
the  instrument  is  varied.  Their  apparatus  is  accurate  to 
about  5  per  cent. 


5.    THE  SILVER  TITRATION  COULOMETER 

The  silver  titration  coulometer  of  Kistiakowsky l  is  some- 
times convenient  where  the  current  does  not  exceed  0.2  ampere 
and  where  the  duration  of  the  experiment  does  not  exceed  an 
hour.  A  silver  anode  is  dissolved  in  a  10  per  cent  potassium 
nitrate  solution  by  the  passage  of  the  current,  and  is  then 
titrated.  In  the  improved  form  the  silver  anode  is  at  the 
bottom  of  a  tube  18  to  22  centimeters  long,  3.5  centimeters  in 
diameter  at  the  top,  and  1  centimeter  at  the  bottom.  The 
cathode  is  of  copper  and  dips  in  a  7  per  cent  copper  nitrate 
solution  to  which  ^  of  its  volume  of  a  10  per  cent  potassium 

9  Phil.  Mag.  35,  334,  (1868). 

10  Proc.  Royal  Dublin  Soc.  7,  559,  (1892). 

11  Z.  f.  Elektroch.  7,  259,  (1901). 

12  Z.  f.  Elektroch.  7,  421,  (1901). 

i  Z.  f.  Elektroch.  12,  713,  (1906). 


12 


APPLIED    ELECTROCHEMISTRY 


nitrate  solution  has  been  added.  This  solution 
is  contained  in  a  porous  cup  at  the  top  of  the 
tube.  After  the  experiment  the  potassium 
nitrate  solution  containing  the  dissolved  sil- 
ver is  drawn  off  and  titrated  with  0.02  normal 
potassium  thiosulphate,  and  a  saturated  iron 
alum  solution  as  indicator.  The  error  of  a 
single  determination  may  amount  to  0.5  per 
cent. 

In  the  original  form,  which  is  the  one  still 
generally  used,  the  cathode  is  of  platinum  and 
dips  into  a  J  to  ^  normal  solution  of  nitric  acid. 
The  division  between  the  acid  and  the  nitrate 
is  shown  in  Figure  7  by  the  dotted  line.  In 
order  to  have  the  silver  dissolve  with  100  per 
cent  efficiency,  it  should  be  freshly  deposited 
electrolytically  ; 2  also,  all  of  the  anode  should 
be  the  same  distance  from  the  cathode,  as  shown 
in  the  figure ;  otherwise  the  current  density  will 
be  too  great  on  the  part  nearest  the  cathode,  and 
bubbles  of  gas  may  be  given  off.  It  is  conven- 
ient to  have  the  anode  made  of  a  platinum  spiral 
of  the  form  shown,  on  which  a  little  more  silver 
is  deposited  electrolytically  before  a  measure- 
be  dissolved  off  in  the  measure- 

tion  coulometer     ment. 


F££^S:  ment  than 


2  Ostwald-Luther,  Hand-  und  Hiilfsbuch,  3d  ed.  p.  600,  (1910). 


CHAPTER   II 

ELECTROCHEMICAL   ANALYSIS 
1.     NONELECTROLYTIC    METHODS 

THERE  are  four  different  electrical  methods  of  quantitative 
analysis.  These  are  (1)  potential  measurements,  which  give  a 
means  of  determining  the  concentrations  of  ions  too  dilute  to 
determine  gravimetrically  ;  (2)  conductivity  measurements, 
which  is  a  method  very  convenient  for  determining  concentra- 
tions of  solutions;  (3)  titration  with  a  galvanometer  in  place 
of  an  ordinary  indicator,  and  finally  (4)  the  ordinary  electro- 
analysis,  in  which  the  metal  is  deposited  on  a  platinum  electrode 
and  weighed. 

The  principle  of  the  first  method,  originally  pointed  out  by 
Ostwald,1  is  as  follows  :  Suppose  the  concentration  of  silver 
chloride  in  its  saturated  solution  is  desired.  If  the  electro- 
motive force  of  the  cell 

Ag  |  TV  NAgN03  1  TV  NKN03  1  saturated  solution  of  AgCl  |  Ag 

were  measured,  and  the  concentration  ^  of  the  silver  ions  in 
the  nitrate  were  known,  as  it  is  from  conductivity  measure- 
ments, the  concentration  cz  of  the  silver  chloride  ions  could  be 
computed  by  the  Nernst  formula 


In  practice  some  conducting  salt  is  added  to  the  silver  chloride 
solution  in  order  to  lower  the  resistance  of  the  cell.     If  potas- 

i  Lehrbuch,  2d  ed.  II,  879. 
13 


14  APPLIED   ELECTROCHEMISTRY 

sium  chloride  is  chosen,  the  solubility  of  silver  chloride  is 
reduced,  but  its  value  in  pure  water  can  be  computed  from  this 
result.2  If  potassium  nitrate  were  used,  no  reduction  in  the 
solubility  would  take  place.  Where  the  concentration  of  the 
salt  is  so  small,  the  ion  concentration  is  very  nearly  equal  to 
the  total  concentration  on  account  of  the  fact  that  the  salt  is 
nearly  100  per  cent  dissociated.  Other  instances  where  this 
method  of  measuring  ion  concentrations  has  been  found  use- 
ful are  in  the  determination  of  the  solubility  of  mercurous 
chloride  from  the  electromotive  force  of  the  cell : 

Hg  |  Hg.CI,  in  TV  NKC1 1  TV  NHg2N2O6  +  HNO3 1  Hg, 

and  from  this  result  the  solubility  of  mercurous  sulphate  from 
the  electromotive  force  of  the  cell,3 

""°^  'Hg. 


and     NKNO 


and     NKNO 


These  examples  are  sufficient  to  illustrate  the  method.  Some 
of  the  errors  that  attend  these  measurements  may  now  be  men- 
tioned. One  difficult}''  is  to  get  different  electrodes  of  the 
same  metal  to  show  exactly  the  same  electromotive  force  when 
placed  in  the  same  solution  of  one  of  their  salts.  This  seems  to 
depend  on  the  surface  of  the  metal,  and  some  method  has  to  be 
used  to  make  them  as  nearly  identical  as  possible.  This  can 
often  be  accomplished  by  using  an  electrode  covered  electrolyti- 
cally  with  a  layer  of  the  metal,  or  if  the  metal  is  more  electro- 
positive than  mercury,  amalgams  of  equal  concentrations  may 
be  used.4  The  electrolytic  solution  pressure  is  thereby  some- 
what changed,  but  by  the  same  amount  for  each  electrode,  and 
since  the  electrolytic  solution  pressure  drops  out,  the  resulting 
electromotive  force  is  unaffected.  Another  method  of  obtaining 
constant  results  is  to  use  the  metal  in  a  finely  divided  form. 
This  may  be  done  by  depositing  electrolytically  with  a  high- 
current  density  or  by  decomposing  some  compound  of  the  metal 

a  Goodwin,  Z.  f.  phys.  Ch.  13,  641,  (1894). 
«  Wilsmore,  Z.  f.  phys.  Ch.  35,  20,  (1900). 
4  Goodwin,  I.e.  p.  676. 


ELECTROCHEMICAL   ANALYSIS  15 

in  question.5  Another  source  of  error  is  the  potential  at  the 
junction  of  the  different  solutions,  but  this  can  generally  be 
either  calculated  or  reduced  to  an  insignificant  amount  by 
adding  some  indifferent  salt 6  or  by  connecting  the  liquids  with 
saturated  solutions  of  potassium  chloride7  or  ammonium  nitrate.8 

A  method  based  on  potential  measurement  has  been  worked 
out  for  determining  the  amount  of  carbonic  acid  in  gases.9  The 
gas  bubbles  through  a  solution  of  bicarbonate,  and  the  result- 
ing hydrogen  ion  concentration  of  the  solution  is  determined  by 
potential  measurements,  from  which  the  partial  pressure  of  the 
carbonic  acid  can  be  computed. 

The  principle  involved  in  determining  the  amount  of  sub- 
stance in  a  solution  by  conductivity  measurement 10  is  the 
same  as  when  any  other  physical  property,  such  as  specific 
gravity,  is  used  for  the  purpose ;  that  is,  the  relation  between 
the  conductivity  and  quantity  of  substance  in  solution  must  be 
known.  These  data  have  already  been  obtained  in  a  large 
number  of  cases  and  have  been  collected  by  Kohlrausch  and  Hol- 
born.  If  the  solution  contains  a  single  electrolyte  whose  con- 
ductivity at  given  concentrations  has  already  been  determined,  all 
that  is  necessary  is  to  interpolate  graphically  or  arithmetically 
in  the  table.  If,  however,  there  is  a  maximum  conductivity,  as 
in  the  case  of  sulphuric  acid,  there  would  be  two  possible  con- 
centrations for  a  given  value  of  the  conductivity.  It  is  easy 
to  tell  on  which  side  of  the  maximum  such  a  solution  lies  by 
diluting  a  little  and  redetermining  the  conductivity.  If  the 
solution  were  more  dilute  than  corresponds  to  the  maximum 
value,  further  dilution  would  decrease  the  conductivity  ;  if  less 
dilute,  the  conductivity  would  be  increased.  In  case  the  solu- 
tion has  a  concentration  near  that  of  maximum  conductivity, 

5  Richards  and  Lewis,  Z.  f.  phys.  Ch.  28,  1,  (1899)  ;  also  Lewis,  J.  Am.  Chem. 
Soc.  28,  158,  (1905). 

6  Bugarszky,  Z.  f.  anorg.  Ch.  14,  150,  (1897). 

7  Bjerrum,  Z.  f.  phys.  Ch.  53,  428,  (1905). 

8  Gumming,  Z.  f.  Elektroch.  13,  17,  (1907). 

9  Bodlander,  Jahrb.  d.  Elektroch.  11,  499,  (1904). 

10  See  Kohlrausch  and  Holborn,  Das  Leitvermogen  der  Elektrolyte,  p.  124, 
(1898). 


16  APPLIED   ELECTROCHEMISTRY 

where  the  determination  would  be  inaccurate,  it  can  be  diluted 
enough  to  remove  it  from  this  point,  and  the  contents  of  the 
new  solution  determined.  From  this  the  concentration  in 
the  original  one  can  be  calculated. 

This  method  has  been  shown  to  be  useful  in  the  determina- 
tion of  impurities  in  sugar  and  of  mineral  waters.11  On  account 
of  the  fact  that  the  equivalent  weights  of  the  impurities  likely 
to  be  present  in  mineral  waters  vary  only  within  certain  limits, 
it  has  been  found  that  the  quantity  of  the  impurities  can  be 
estimated  with  a  fair  degree  of  accuracy  from  conductivity 
without  analyzing  the  water  to  see  which  of  the  usual  impurities 
are  present. 

This  method  is  also  useful  in  the  case  of  mixtures  of  two 
salts  when  the  conductivity  of  the  mixture  is  the  arithmetical 
mean  of  the  single  conductivities.  This  is  often  the  case  with 
nearly  related  compounds,  which  are  generally  difficult  to  sepa- 
rate chemically.  For  two  substances  for  which  this  rule  holds, 
having  at  equal  concentrations  the  specific  conductivities  K± 
and  jfiQ,  the  conductivity  of  a  mixture  of  the  same  total  concen- 
tration would  have  the  conductivitv  K  =  K\P\  + KiP*.  By 

Pi+Pt 
this  means  it  has  been  found  possible  to  analyze  satisfactorily 

mixtures  of  potassium  chloride  and  bromide,  and  sulphates  of 
potassium  and  rubidium.12  Conductivity  has  also  been  applied 
extensively  for  the  determination  of  the  solubility  of  very 
insoluble  salts.10 

The  use  of  a  galvanometer  as  an  indicator  depends  for  the 
end  point  either  on  a  sharp  change  in  the  resistance  of  the  cell 
containing  the  solution  titrated  or  in  the  change  in  the  electro- 
motive force  on  electrodes  dipping  in  this  solution.  An  example 
of  the  first  case  is  the  titration  of  silver  nitrate  with  a  standard 
solution  of  potassium  chloride.13  A  measured  quantity  of  a 
standard  solution  of  potassium  chloride  is  placed  in  a  beaker 
with  two  silver  electrodes.  In  series  with  the  two  electrodes 

u  Reichert,  Z.  f.  anal.  Ch.  28,  1,  (1889). 

12  Erdmann,  B.  B.  30,  1175,  (1897). 

18  Salomon,  Z.  f.  Elektroch.  4,  71,  (1898). 


ELECTROCHEMICAL   ANALYSIS  17 

are  connected  a  galvanometer  and  a  source  of  electromotive 
force,  which  must  be  less  than  the  decomposition  value  of  the 
potassium  chloride.  On  closing  the  circuit,  only  a  very  small 
residual  current  will  be  detected.  On  adding  a  little  of  the 
silver  nitrate  to  the  solution,  silver  chloride  is  precipitated,  and 
a  certain  amount  of  silver  ions,  corresponding  to  the  solubility 
of  the  chloride,  will  be  in  solution.  We  now  have  the  cell 

Ag  |  AgCl  solution  |  Ag, 

which  has  no  decomposition  point,  but  the  quantity  of  silver  is 
so  small  that  the  large  resistance  prevents  the  current  from 
increasing  to  any  great  extent.  As  nitrate  is  added,  the 
quantity  of  silver  in  solution  changes  very  little  until  the  last 
of  the  potassium  chloride  is  used  up.  The  first  drop  of  silver 
nitrate  in  excess  now  increases  the  silver  ions  enormously,  and 
there  is  a  corresponding  large  increase  in  current,  due  to  the 
reduced  resistance  of  the  cell.  The  following  table  shows  the 
sharpness  of  the  change  : 13 


CUBIC  CENTIMETERS  OF  AoNO8 

GALVANOMETER  BEADING 

3.00 

15 

4.40 

20 

5.00 

16 

5.50 

21 

5.60 

20 

5.65 

42 

The  use  of  a  galvanometer  as  indicator  when  the  electro- 
motive force  changes  suddenly  at  the  end  point  is  illustrated  by 
the  following  examples  : 14  Suppose  two  beakers,  one  containing 
a  tenth  normal  solution  of  mercurous  nitrate,  the  other  a  definite 
quantity  of  mercurous  nitrate  solution  to  be  titrated,  are  con- 
nected by  a  siphon  containing  tenth  normal  potassium  nitrate. 
The  bottom  of  each  beaker  is  covered  with  a  layer  of  mercury 
which  makes  contact  with  a  platinum  wire  sealed  in  the  glass. 

w  Behrend,  Z.  f.  phys.  Ch.  11,  482,  (1893). 


18  APPLIED   ELECTROCHEMISTRY 

Such  a  cell  would  have  the  electromotive  force  R T  log  -l,  where 

'2 

el  is  the  concentration  of  the  mercury  ions  in  the  tenth  normal 
solution  and  cz  is  their  concentration  in  the  unknown  solution. 
If  tfj  is  equal  to  c2,  the  electromotive  force  would  be  zero,  but 
in  general  el  and  <?2  would  be  somewhat  different,  so  that  there 
would  be  a  reading  in  a  galvanometer  connected  across  the 
terminals  of  the  cell.  If  a  standard  solution  of  potassium 
chloride  is  now  added  from  a  burette  to  the  unknown  solution, 
the  concentrated  <?2  will  be  diminished,  due  to  the  precipitation 
of  the  mercury,  and  consequently  the  electromotive  force  will 
increase.  As  the  end  point  is  approached  the  change  in  electro- 
motive force  for  each  drop  of  potassium  chloride  added  will 
be  greater  and  greater,  because  of  the  larger  percentage  change 
in  the  concentration.  With  the  drop  of  chloride  which  throws 
out  the  last  of  the  mercury,  the  percentage  change  will  be  the 
greatest  of  all,  and  there  will  be  a  corresponding  change  in 
the  reading  of  the  galvanometer.  The  quantity  of  mercury  ions 
now  in  the  solution  is  due  to  the  solubility  of  the  mercunr 
chloride.  Since  this  solubility  is  diminished  by  adding  a  salt 
with  a  common  ion,  the  electromotive  force  will  continue  to 
increase  slowly  on  adding  more  chloride,  but  no  further  sudden 
change  will  occur.  This  change  then  indicates  the  end  point. 
It  is  evident  that  this  method  would  serve  equally  well  to 
determine  the  strength  of  the  chloride  and  that  the  titration  can 
be  carried  out,  starting  with  potassium  chloride  in  one  beaker  in 
place  of  mercury  nitrate.  In  this  case  there  would  be  a  decrease 
in  voltage  at  the  end  point  instead  of  an  increase.  Bromides 
can  be  titrated  as  well  as  chlorides,  but  a  sharp  end  point  is  not 
obtained  with  iodides. 

Since  the  determination  of  the  end  point  depends  on  the 
concentration  of  the  ions,  the  final  volume  of  the  solution  must 
be  kept  within  such  limits  that  a  drop  of  the  solution  from  the 
burette  will  cause  a  marked  change  in  the  galvanometer  read- 
ing. Starting  with  tenth  normal  solutions,  for  this  reason  the 
final  volume  should  not  exceed  30  cubic  centimeters,  and 
therefore  not  over  10  cubic  centimeters  of  the  unknown 


ELECTROCHEMICAL   ANALYSIS 


19 


solution  should  be  taken  for  analysis.  Since  the  end  point 
can  be  obtained  only  to  0.05  cubic  centimeter,  this  means  an 
accuracy  of  0.5  per  cent.  In  titrating  potassium  chloride  the 
change  in  voltage  at  the  end  point  is  from  0.1  to  0.15  volt;  in 
the  case  of  the  bromide  it  is  0.2  volt.  Silver  electrodes  and 
silver  nitrate  can  be  used  in  place  of  mercury  and  mercury 
nitrates,  and  by  this  arrangement  it  is  possible  to  determine 
directly  the  iodine  in  the  presence  of  chloride  and  bromide,  if 
an  ammoniacal  solution  is  used.  Silver  iodide,  unlike  silver 
chloride  and  bromide,  is  nearly  insoluble  in  ammonia.  There- 
fore on  adding  silver  nitrate  to  an  ammoniacal  solution  of 
potassium  chloride,  bromide,  and  iodide,  only  the  silver  iodide 
will  precipitate.  When  all  the  silver  iodide  is  precipitated, 
there  is  a  sudden  change  in  the  galvanometer  reading.  On 
acidifying,  the  combined  amount  of  chloride  and  bromide  may 
be  determined.  If  also  the  total  quantity  of  silver  chloride, 
bromide,  and  iodide  is  weighed,  the  original  amount  of  potas- 
sium chloride,  bromide,  and  iodide  can  be  calculated.  This 
procedure,  however,  is  not  very  accurate  for  the  chloride  and 
bromide,  as  is  shown  by  the  following  analyses.14 


GRAMS  TAKEN 

AMOUNT  FOUND 

GRAMS  TAKEN 

AMOUNT  FOUND 

KC1 

0.0223 

0.0246 

K€l 

0.0448 

0.0431 

KBr 

•  0.0359 

0.0314 

KBr 

0.0354 

0.3800 

KI 

0.0662 

0.0666 

KI 

0.0167 

0.0169 

0.1244 

0.1226 

0.0969 

0.0980 

An  exactly  similar  method  has  been  shown  to  be  useful  in 
the  titration  of  acids  and  bases.15  Neglecting  the  small  poten- 
tials due  to  the  liquid-liquid  junctions,  the  electromotive  force 
of  the  cell 


II. 


acid  of 


cone,  c 


is  given  by  the  equation 


neutral  salt 


e=  ETlog- 


acid  of 
cone.  <?2 


W.  Bottger,  Z.  f.  phys.  Ch.  24,  253,  (1898). 


20  APPLIED   ELECTROCHEMISTRY 

assuming  complete  dissociation.  If  alkali  is  now  added  to 
one  of  these  acids,  the  hydrogen  ion  concentration  diminishes, 
causing  a  gradual  increase  in  the  electromotive  force.  As  in 
the  cases  described  above,  there  will  be  a  sudden  change  in  the 
galvanometer  reading  when  the  end  point  is  reached.  The 
hydrogen  electrode  is  shown  in  Figure  8,  and  consists  of  palla- 
dium-plated gold,  which  gives  more  constant  val- 
OrV —  ues  than  platinized  platinum.  The  concentration 
(f  of  the  hydrogen  soon  becomes  constant  in  the 
electrode,  as  it  is  not  absorbed  by  the  gold  at  all. 
In  place  of  a  hydrogen  electrode  as  standard  in 
the  above  cell,  a  normal  electrode  would  do 
equally  well. 

In  carrying  out  a  titration,  the  acid  or  alkali  to 
be  titrated  is  placed  in  a  beaker  and  the  hydrogen 
electrode  put  in  position  so  that  the  palladium - 
plated  gold  is  partly  immersed.  This  electrode 
is  then  connected  with  the  standard  electrode  and 
with  some  means  for  measuring  the  electromotive 
force;  for  example,  a  Lippmann  electrometer  and 
slide  wire  bridge.  Hydrogen  is  then  bubbled 
Fgen8eilcu-ode°"  over  tne  hydrogen  electrode  till  a  constant  poten- 
tial is  reached,  which  should  require  only  a  few 
minutes,  and  then  alkali  or  acid,  as  the  case  may  be,  is  added 
from  the  burette.  After  each  addition  the  liquid  is  stirred  up 
and  the  potential  measured.  This  will  be  found  to  increase 
gradually  till  the  end  point  is  reached,  where  there  will  be  a 
sudden  change  in  the  potential. 


2.     ELECTROLYTIC  METHODS 

The  methods  of  analysis  described  above  have  not  come  into 
general  use.  The  electrolytic  method,  on  the  contrary,  is  ex- 
tensively employed,  and  in  some  cases  has  entirely  displaced 
other  methods.  It  consists  in  depositing  by  electrolysis  the 
substance  to  be  determined  on  one  of  the  electrodes  in  a  form 
that  can  be  dried  and  accurately  weighed.  A  number  of 


ELECTROCHEMICAL   ANALYSIS 


21 


different  cases  may  be  distinguished.  A  metal  is  usually 
deposited  on  the  cathode  in  the  pure  state  or  in  a  mercury 
cathode  as  an  amalgam.  Lead  and  manganese  are  exceptional 
in  that  they  are  deposited  on  the  anode  as  peroxide.  By  the 
use  of  a  silver  anode,  chlorine,  bromine,  and  iodine  may  be 
obtained  and  weighed  as  the  chloride,  bromide,  and  iodide  of 
silver,  though  such  determinations  are  not  often  carried  out. 

The  possibility  of  electroanalysis  was  first  pointed  out  by 
Cruikshank  in  1801.  It  was  very  little  used,  however,  until 
subsequent  to  the  work  of  Wolcott  Gibbs  on  the  electroanalysis 
of  copper  and  nickel  in  1864.1'  It  has  since  formed  the  subject 
of  a  great  number  of  investigations  and  has  been  employed 
extensively  in  analytical  laboratories.  A  considerable  number 
of  improvements  have  been  made  in  electroanalytical  methods 
during  this  time.  One  of  the  greatest  of  these  is  the  saving  of 
time  by  stirring  the  solution  during  the  electroanalysis,  in 
place  of  trusting  to  electrolytic  migration  and  diffusion  to 
bring  the  ions  to  the  electrode  on  which  they  are  to  be 
deposited.  Table  3  gives  an  idea  of  the  difference  in  time 
required  for  analyses  with  and  without  stirring.2 


TABLE  3 

Average  Duration  of  Electroanalysis  with  and  without  Stirring 


METAL 

TIME  IN  MINUTES  WITHOUT 
STIRRING 

TIME  IN  MINUTES  WITH 
STIRRING 

Nickel 

180 

40 

Zinc 

120 

15 

Copper 
Cadmium 

360 
180 

20 
10 

Lead 

60 

15 

Silver 

180 

15 

Mercury 
Antimony 
Tin 

105 
105 
360 

15 
30 

20 

1  A.  Fischer,  Elektrolytische  Schnellmethoden,  p.  11,  (1908). 

2  A.  Fischer,  I.e.  p.  13. 


22 


APPLIED   ELECTROCHEMISTRY 


A  second  improvement  consists  in  increasing  the  number  of 
metals  that  can  be  determined  electrolytically,  by  substituting 
a  mercury  for  a  platinum  cathode.  Mercury  was  first  sug- 
gested for  this  purpose  by  Wolcott  Gibbs,3  but  not  much  atten- 
tion has  been  paid  to  its  use  until  recently.  With  a  mercury 
cathode  the  metal  deposited  is  dissolved  by  the  mercury  and  is 
weighed  as  an  amalgam.  E.  F.  Smith  showed  that  even  the 
highly  electropositive  metals  belonging  to  the  alkali  arid  alka- 
line earth  groups  can  be  determined  by  this  means.3 

In  order  to  explain  the  theory  of  electroanalysis,  an  acid 
sulphate  solution  of  some  metal  standing  below  hydrogen  in 
the  electromotive  series,  given  in  Table  4,  will  first  be  con- 
sidered.4 The  concentration  of  the  hydrogen  ions  and  metallic 
ions  is  assumed  to  be  one  gram  ion  per  liter. 

TABLE  4 

Electrolytic  Single  Potential  Differences  between  Elements  and  a  Solution  contain- 
ing one  Gram  Ion  of  the  Element  per  Liter.  The  Normal  Electrode  on  the  Scale 
Chosen  =  —0.56  volt 


Magnesium 2.26? 

Aluminum +0.999? 

Manganese +0.798 

Zinc +0.493 

Cadmium +0.143 

Iron +0.165 

Thallium +0.045 

Cobalt +  0.173 6 

Nickel      ......  +0.3236 

Tin      ..."....  <- 0.085 

Lead -0.129 

Hydrogen -0.277 

Copper      ....  -0.606 


Arsenic <  — 0.57 

Bismuth <- 0.668 

Antimony <- 0.743 

Mercury —1.027 

Silver -1.075 

Palladium      .....  <- 1.066 

Platinum <  -1.140 

Gold <- 1.356 

Chlorine —1.680 

Bromine —1.372 

Iodine -0.905 

Oxygen     ......       -0.670 


Suppose  two  platinum  electrodes  are  dipping  in  this  solution, 
and  that  a  gradually  increasing  electromotive  force  is  applied. 

8  E.  F.  Smith,  Electroanalysis,  p.  65,  (1907). 

4  Le  Blanc,  Electrochemistry,  English  translation,  p.  248,  (1907). 

6  Calculated  from  Richards  and  Behr,  Carnegie  Institution  of  Washington, 
publication  No.  61,  p.  31,  on  the  assumption  that  normal  FeSO4  is  24  per  cent 
dissociated.  e  Approximately. 


ELECTROCHEMICAL   ANALYSIS  23 

At  first  only  a  small  diffusion  current  will  flow,  but  when  the 
decomposition  voltage  of  the  salt  is  reached,  electrolysis  will 
begin.  The  decomposition  point  is  the  sum  of  the  potential 
differences  at  the  anode  and  the  cathode.  Since  the  sulphate 
radical  does  not  escape  from  the  solution,  the  potential  at  the 
anode  will  remain  nearly  constant  during  the  electrolysis,  and 
the  potential  at  the  cathode  at  the  decomposition  point  is  equal 
to  the  potential  which  the  precipitating  metal  would  itself 
have  in  the  solution.7  This  will  be  clear  from  the  following 
considerations.8  Suppose  a  metallic  electrode  dips  in  a  solu- 
tion of  one  of  its  salts  in  which  the  osmotic  pressure  of  the 
ions  of  the  metal  is  p.  There  will  be  a  certain  tendency  for 
the  metal  to  go  into  solution  as  ions,  called  the  electrolytic 
solution  pressure,  which  will  be  designated  by  P.  Suppose 
that  P  is  less  than  p,g  as  must  be  the  case  if  the  metal  stands 
below  hydrogen.  A  certain  amount  of  the  ions  of  the  metal 
will  then  be  deposited  on  the  electrode,  charging  the  solution 
negatively  and  the  electrode  positively.  The  metallic  ions  in* 
solution  will  then  be  repelled  by  the  positively  charged  elec- 
trode with  a  force  &,  increasing  with  the  quantity  of  metal 
deposited.  This  force  finally  becomes  so  great  that  equilib- 
rium is  established  according  to  the  following  equation  : 


The   potential  difference  between  the    electrode   and  solution 
is  then  given  by  the  equation 

RT,       P 


where  R  is  the  gas  constant,  T  the  absolute  temperature,  n  the 
valence  of  the  metal,  and  F  the  electrochemical  constant.  Sup- 
pose now  the  force  k  is  diminished  slightly  by  applying  an 
external  electromotive  force  in  a  direction  tending  to  deposit 
the  metallic  ions  on  the  electrode.  The  value  of  e  will  be 

7  Le  Blanc,  Z.c.  p.  219. 

8  See  H.  M.  Goodwin,  Z.  f.  phys.  Ch.  13,  579,  (1894). 

9  There  will  be  no  change  in  the  method  of  the  demonstration  if 


24  APPLIED   ELECTROCHEMISTRY 

changed  only  slightly  from  that  given  by  the  equation  above, 
but  the  metal  will  be  deposited  continuously,  because  the  sum 
of  the  forces  P  and  k,  tending  to  send  the  metal  in  solution, 
is  now  slightly  less  than  the  force  jt?,  tending  to  cause  the 
metal  to  deposit. 

As  the  ions  of  the  metal  become  more  dilute,  p  becomes  less, 
and  the  potential  difference  e,  as  well  as  the  decomposition 
voltage  of  the  solution,  will  consequently  increase  in  value. 
The  potential  difference  between  the  solution  and  the  cathode 
eventually  becomes  so  great  that  the  value  necessary  for  the 
deposition  of  hydrogen  is  reached.  This  potential  difference, 
eh,  is  given  by  the  equation 


where  77  is  the  overvoltage  of  hydrogen  on  the  metal  deposit- 
ing. After  this  condition  has  been  reached,  the  metal  and 
hydrogen  are  deposited  simultaneously.  The  following  rela- 
tion then  holds  as  long  as  the  electrolysis  continues  : 


If  electrolysis  is  continued,  the  overvoltage  77  gradually  in- 
creases, due  to  the  increasing  proportion  of  the  current  used 
to  liberate  hydrogen,10  and  consequently  p  becomes  less.  It  is 
evident  that  the  reduction  can  never  be  absolutely  complete, 
for  if  p  =  0,  e  would  be  infinite. 

RT        P 

From   the    equation   e  =  -  loef  £».,    it    is    evident    that   to 

nF          p 

reduce  the  quantity  of  metal  in  solution  to  a  negligible 
amount,  —  for  example,  to  j$fa$  °^  ^ie  original  quantity,  — 


7?  T 

the  increase  in  voltage  at  the  cathode  will  be  e  —  —  log  10000 

F 

=  0.23  volt  for  a  monivalent  metal,  or  half  this  value  for  a 
bivalent  metal.  Monivalent  and  bivalent  metals  must  there- 
fore stand  respectively  0.23  volt  and  0.12  volt  below  the 

10  F.  Foerster,  Elektrochemie  w&jseriger  Losungen,  p.  183. 


ELECTROCHEMICAL   ANALYSIS  25 

potential  at  which  hydrogen  would  be  deposited  on  the  metal 
in  question  in  order  to  be  so  completely  separated  from  the 
solution  considered. 

In  consequence  of  overvoltage  and  of  the  possibility  of  re- 
ducing the  concentration  of  hydrogen  ions,  the  potential  dif- 
ference at  which  hydrogen  is  deposited  may,  under  certain 
conditions,  be  very  much  greater  than  that  given  in  table  of 
electrolytic  potentials.  Consequently,  metals  standing  above 
hydrogen  in  the  electrolytic  series  can  be  deposited  in  case  the 
overvoltage  of  metal  in  question  is  high  and  the  concentration 
of  the  hydrogen  ions  is  low. 

It  is  evident  from  what  has  been  said  that  hydrogen  plays  an 
important  role  in  electrolysis.  It  acts  as  a  safety  valve  in  pre- 
venting the  potential  difference  at  the  cathode  from  rising 
above  a  certain  value.  This  value  depends  on  the  concentra- 
tion of  the  hydrogen  ions  and  on  the  overvoltage,  and  it  is 
therefore  possible  to  vary  this  maximum  voltage  by  changing 
the  concentration  of  the  hydrogen  ions.  For  example,  the  po- 
tential difference  of  a  hydrogen  electrode  in  a  normal  acid  solu- 
tion differs  by  0.81  volt  from  a  hydrogen  electrode  in  a  normal 
alkali  solution.11  The  lower  the  concentration  of  the  hydrogen 
ions,  the  higher  will  be  the  voltage  necessary  to  deposit  hydro- 
gen, and  for  this  reason  solutions  of  low  hydrogen  ion  concen- 
tration must  be  employed  for  depositing  electropositive  metals. 
Such  solutions  are  those  containing  ammonia,  ammonium,  or 
sodium  sulphide,  and  potassium  cyanide.  In  these  solutions 
the  metals  form  complex  salts,  and  the  concentration  of  their 
ions  is  greatly  reduced,  and  a  greater  potential  difference  is 
also  required  to  deposit  metals  from  such  solutions  than  from 
solutions  of  their  simple  salts.  Solutions  of  complex  salts  are 
of  great  importance  in  electroanalysis ;  some  metals,  such  as 
iron,  nickel,  antimony,  and  tin,  can  be  reduced  quantitatively 
only  from  such  solutions.12 

Two  metals  can  in  general  be  separated  in  an  acid  solution 
when  they  stand  in  opposite  sides  of  hydrogen  in  the  electro- 
lytic series,  for  the  hydrogen  prevents  the  cathode  potential 

11  Le  Blanc,  I.e.  p.  209.  12  Fischer,  I.e.  p.  31. 


26  APPLIED   ELECTROCHEMISTRY 

difference  from  becoming  great  enough  to  deposit  the  metal 
standing  above  hydrogen.  When  both  metals  are  below  hydro- 
gen, they  can  sometimes  be  separated  by  keeping  the  voltage 
below  that  necessary  to  deposit  the  more  electropositive  metal.13 
As  explained  above,  if  the  metal  to  be  reduced  is  monivalent, 


FIG.  9.  —  Platinum  dish  for  electroanalysis 

the  potential  difference  between  it  and  the  solution  must  be  at 
least  0.23  volt  less  than  that  of  the  metal  from  which  it  is  to  be 
separated,  while  for  a  bivalent  metal  a  difference  of  only  0.12 


13  Le  Blanc,  I.e.  p. 


ELECTROCHEMICAL   ANALYSIS 


27 


volt  is  necessary.  This  applies  only  when  the  two  metals  do 
not  alloy  with  each  other ;  if  they  form  an  alloy,  the  decompo- 
sition point  of  each  is  affected  by  the  presence  of  the  other. 
For  this  reason  it  is  difficult  to  separate  mercury  from  other 
metals.14 

The  above  theory  makes  no  attempt  to  explain  why  some 
metals  deposit  in  a  compact  form  and  why  others  do  not.  This 
is  a  very  important  question  in  electroanalysis  ;  for  if  the  deposit 
does  not  adhere  well  to  the  cathode,  it  cannot  be  washed  and 


FIG.  10.  —  Platinum  gauze  cathode  for  electroanalysis 

weighed.  The  structure  of  the  deposit  depends,  first  of  all,  on 
the  nature  of  the  metal  itself.  Some  metals,  such  as  zinc, 
cadmium,  and  bismuth,  have  a  tendency  to  deposit  in  a  spongy 
form.  Others,  among  which  is  silver,  deposit  in  large  crystals. 
The  character  of  the  dissolved  salt  from  which  a  metal  is  de- 
posited is  of  great  influence  on  the  properties  of  the  deposit. 
In  general,  metals  are  deposited  in  a  compact,  smooth  layer  from 

w  Fischer,  I.e.  p.  37. 


28 


APPLIED   ELECTROCHEMISTRY 


solutions  of  a  complex  salt,  which  is  frequently  the  only  reason 
for  using  them. 

The  temperature  of  the  solution  in  electroanalysis  is  of  great 


Fio.  11.  —  Mercury  cathode  for  electroanalysis 

importance  in  the  case  of  complex  salts.  The  velocity  with 
which  the  ions  are  produced  from  the  complex  is  not  so  rapid 
as  from  the  simple  salt,  but  this  velocity  is  increased  by  an  in- 


ELECTROCHEMICAL    ANALYSIS  29 

crease  in  the  temperature.15  In  general,  the  more  complex  the 
salt,  the  greater  is  the  effect  of  high  temperature  in  accelerating 
the  reduction. 

The  apparatus16  commonly  used  in  electroanalysis  consists  in 
a  platinum  dish  cathode  6  centimeters  in  diameter  and  3 
centimeters  deep.  Figure  9  represents  such  a  dish  with  a 
rotating  anode.  In  place  of  a  dish,  the  cathode  may  be 
platinum  gauze.  In  this  case  the  liquid  to  be  analyzed  is  held 
in  a  beaker  or  separatory  funnel,  as  shown  in  Figure  10.  Figure 
11  represents  an  arrangement  for  using  a  mercury  cathode.  A 
beaker  of  50  cubic  centimeters'  capacity  has  a  platinum  wire 
sealed  into  the  bottom  by  which  contact  is  made  with  the  mer- 
cury and  the  copper  plate  on  which  the  beaker  is  placed. 

15  Fischer,  I.e.  p.  34. 

16  The  illustrations  are  taken   from  Edgar  F.  Smith's  Electroanalysis,  P. 
Blakiston's  Son  and  Company  (1907). 


CHAPTER  III 

ELECTROPLATING,  ELECTROTYPING,  AND  THE  PRODUCTION 
OF  METALLIC  OBJECTS 

1.    ELECTROPLATING 

THE  object  of  electroplating  is  to  cover  a  metal  with  a  layer 
of  another  metal  for  the  purpose  of  improving  its  appearance 
and  durability.  The  principal  metals  used  for  the  coating  are 
nickel,  copper,  zinc,  brass,  silver,  and  gold. 

In  plating,  the  first  step  is  to  clean  the  surface  thoroughly,  in 
order  to  make  the  deposited  coating  adhere  well.  In  case  the 
surface  is  rough,  it  must  be  ground  smooth  and  polished  on  a 
suitable  buffing  wheel.  The  next  operation  is  the  removal  of 
the  grease  and  oxide  from  the  surface.  The  grease  is  removed 
by  dipping  in  a  hot  solution  of  sodium  hydrate  or  carbonate. 
The  alkali  is  then  washed  off,  and  the  object  is  dipped  into  a 
bath  called  a  pickle,  the  purpose  of  which  is  to  remove  the 
oxide  and  to  make  it  bright.  The  pickle  varies  with  the  metal 
to  be  treated,  since  a  solution  which  works  well  with  one  metal 
is  not  necessarily  suited  to  others.  Cast  iron  and  wrought  iron 
are  pickled  in  a  solution  made  by  mixing  1  part  by  weight  of 
concentrated  sulphuric  acid  with  15  parts  of  water.1  A 
suitable  pickle  for  zinc  is  simply  dilute  sulphuric  or  hydrochloric 
acid.  Copper,  brass,  bronze,  and  German  silver  are  treated 
with  a  preliminary  pickle  consisting  of  200  parts  by  weight  of 

1  Langbein,  Electrodeposition  of  Metals,  4th  ed.  p.  162.  The  English 
measures  used  by  Langbein  are  converted  to  the  metric  system  when  quoted. 
Unless  otherwise  stated,  the  formulae  given  for  solutions  in  this  chapter  are  taken 
from  the  above  work. 

30 


ELECTROPLATING  AND  ELECTROTYPING 


31 


nitric  acid  of  specific  gravity  1.33,  1  part  of  common  salt,  and 
1  of  lampblack.  The  last  ingredient  has  for  its  purpose  the 
formation  of  nitrous  acid.  After  all  impurities  are  removed  by 


FIG.  12.  —  Plating  tank 

this  bath,  the  object  is  washed  in  boiling  water  so  that  on  re- 
moval it  will  dry  quickly,  and  it  is  then  immersed  in  a  so-called 
bright  dipping  bath,  to  give  a  bright  surface.  This  is  made  up 
of  75  parts  by  weight  of  nitric 
acid,  of  specific  gravity  1.38, 
100  parts  of  concentrated  sul- 
phuric acid,  and  1  part  of 
common  salt.  The  object  is 
then  washed  off  in  water  and 
put  while  wet  in  the  plating 
bath,  where  all  electrical  con- 


FIG.   13.  —  Tray  for  plating  small 
objects 


nections     should     have     been 

made  so  that  the  plating  begins 

immediately.    Instead  of  the  acid  pickles  following  the  removal 

of  grease  by  alkali,  brass  is  sometimes  pickled  in  a  hot  solution 

of  potassium  cyanide,  which  dissolves  the  oxides,  —  somewhat 


32  APPLIED   ELECTROCHEMISTRY 

more  slowly,  however,  than  the  acid, — but  does  not  alter  the 
original  polish.  After  the  plating  is  finished,  the  object  is 
dipped  in  hot  water  and  put  in  warm  sawdust  to  dry. 

The  tanks  used  for  holding  the  plating  solutions  are  usually 
of  wood  and  are  lined  with  lead  or  a  mixture  of  pitch,  resin, 
and  linseed  oil.  The  anodes  are  hung  on  brass  bars  running 
lengthwise  with  the  tank,  and  the  objects  to  be  plated  are  hung 
on  similar  bars  between  two  rows  of  anodes,  in  order  to  plate 
both  sides  uniformly.  This  is  illustrated  in  Figure  12. 
Small  objects  which  are  to  be  carefully  plated  are  strung  to- 
gether in  rows  on  wires  and  hung  in  the  bath.  Where  not  so 


FIG.  14.  —  Drum  for  holding  small  objects  while  plating 

much  care  is  required,  as  in  the  case  of  small  nails,  it  is  suffi- 
cient to  place  them  in  a  tray,  shown  in  Figure  13,  and  hang 
them  in  the  solution,  or  in  a  drum  whose  sides  are  perforated, 
as  in  Figure  14.  The  drum  turns  on  its  axle  slowly,  and  the 
current  is  conducted  from  the  pile  of  small  objects  to  the  axle 
by  metal  strips.  Of  course  the  tray  or  the  axle  and  metal 
strips  are  also  plated. 

When  plating  is  done  on  a  large  scale,  the  current  required 


ELECTROPLATING  AND  ELECTROTYPING 


33 


34  APPLIED   ELECTROCHEMISTRY 

is  always  supplied  by  a  dynamo,  but  there  are  the  two  other 
following  methods,  sometimes  used  for  small  jobs,  which  do  not 
require  a  battery  or  dynamo.  If  a  metal  is  dipped  into  a  solu- 
tion of  a  salt  of  a  metal  standing  below  it  in  the  electrolytic 
series,  the  more  electropositive  metal  will  go  in  solution  and 
the  more  electronegative  will  be  precipitated  on  the  former.  A 
well-known  example  of  this  is  the  precipitation  of  copper  on 
iron,  when  iron  is  dipped  into  solution  of  copper  sulphate. 
This  is  known  as  plating  by  dipping.  As  soon  as  the  metal  is 
thinly  coated,  the  action,  of  course,  stops.  In  case  the  metal  is 
not  electropositive  enough  to  precipitate  the  one  in  solution, 
the  same  result  can  be  produced  by  connecting  it  with  a  piece 
of  zinc  placed  in  the  solution.  The  zinc  is  dissolved  as  the 
negative  pole  of  a  battery  and  precipitates  the  metal  in  solu- 
tion on  the  cathode,  which  is  the  metal  to  be  plated.  This 
method  is  known  as  plating  by  contact.  Neither  of  these 
methods  is  used  on  a  large  scale. 

Figure  15  shows  the  plating  plant  of  the  National  Cash 
Register  Company,2  where  nickel  plating  with  nickel,  copper, 
silver,  and  zinc  are  all  carried  out. 

Nickel  Plating  l 

Nickel  cannot  be  deposited  from  a  strongly  acid  bath,  since 
it  is  above  hydrogen  in  the  electrolytic  series.  The  solution 
ordinarily  used  consists  of  nickel-ammonium  sulphate  of  the 
formula  NiSO4  •  (NH4)2SO4  •  6  H2O,  with  an  additional  amount 
of  ammonium  sulphate  to  increase  the  conductivity.  The 
exact  proportions  of  the  salts  are  not  important.  Different 
receipts  are  given,  varying  from  25  to  50  parts  of  ammonium 
sulphate  to  50  parts  of  the  double  sulphate,  in  1000  parts  of 
water.  The  solution  is  made  acid  enough  to  redden  litmus 
paper  faintly  by  adding  sulphuric  acid,  or  citric  acid,  as  some 
receipts  specify.  This  slight  acidity  is  supposed  to  give  a 

2  Met.  and  Chem.  Eng.  8,  275,  (1910). 

1  For  an  account  of  the  origin  of  nickel  plating,  see  Adams,  Trans.  Am. 
Electrochem.  Soc.  9,  211,  (1906). 


ELECTROPLATING  AND  ELECTROTYPING         35 

whiter  nickel  than  alkaline  or  neutral  solutions.  Baths  of 
nickel  chloride  may  be  used  for  plating  any  metal  but  iron,  for 
iron  always  rusts  if  plated  in  a  bath  of  this  salt.  The  anodes 
are  of  cast  or  rolled  nickel. 

The  proper  current  density  at  the  cathode  is  0.6  ampere  per 
square  decimeter.  The  whole  surface  will  then  be  perceptibly 
coated  with  nickel  in  two  or  three  minutes,  and  a  few  bubbles 
of  gas  will  come  off  continuously.  If  the  current  is  too  weak, 
the  surface  becomes  discolored.  If  the  current  is  too  strong, 
gas  is  evolved  more  violently,  and  the  color  of  the  nickel  soon 
turns  dark.  In  large  objects  the  current  density  is  not  uniform. 
The  more  deeply  immersed  in  the  solution,  the  stronger  is  the 
current,  so  that  unless  turned  during  plating,  large  objects 
would  receive  a  thicker  coating  on  the  surface  that  is  deepest 
in  the  tank.  Iron  is  sometimes  copper  plated  to  prepare  it  for 
nickel  plating.  This  is  supposed  to  make  the  nickel  adhere 
better,  but  nickel  adheres  perfectly  well  to  iron  if  the  surface 
is  properly  cleaned.2 

Copper  Plating 

The  metals  usually  copper  plated,  such  as  zinc,  iron,  and  tin, 
are  more  electropositive  than  copper.  If  these  are  dipped 
into  a  bath  of  copper  sulphate,  they  are  coated  immediately 
with  copper.  The  copper,  however,  frequently  comes  down  in 
a  spongy  form  that  does  not  adhere  well,  so  that  plating  from 
such  a  bath  is  impossible.  It  is  therefore  necessary  to  reduce 
the  concentration  of  the  copper  ions  to  such  an  extent  that  the 
copper  will  be  relatively  more  electropositive  than  the  metal  to 
be  plated,  without  at  the  same  time  reducing  the  total  amount 
of  copper  in  the  solution.  This  is  accomplished  by  using 
the  double  cyanide  of  copper  and  potassium  of  the  formula 
KCu(CN)2.  The  only  copper  ions  present  come  from  the  dis- 
sociation of  the  anion  Cu(CN)2,  which  is  very  slight.  Copper 
will  therefore  not  be  precipitated  from  this  solution  by  zinc  or 
any  other  metal  that  is  to  be  plated.  The  solution  can  be  made 

2  Langbein,  I.e.  p.  203. 


36  APPLIED   ELECTROCHEMISTRY 

up  by  dissolving  cuprous  cyanide  in  potassium  cyanide  to  form 
a  3  to  8  per  cent  solution,  or  the  double  cyanide  may  be  used. 
In  either  case  0.2  per  cent  potassium  cyanide  and  from  J  to  1 
per  cent  sodium  carbonate  is  added.3  The  object  of  the  car- 
bonate is  probabty  to  increase  the  conductivity,  that  of  the  free 
cyanide  to  dissolve  the  anodes  more  readily.  In  case  the 
cuprous  cyanide  is  prepared  by  starting  with  a  cupric  salt,  the 
latter  must  be  reduced  to  the  cuprous  state  before  adding 
the  cyanide;  otherwise  poisonous  cyanogen  would  be  liberated. 
Sodium  sulphite  is  generally  used  for  this  purpose.  The 
copper  cyanide  bath  is  heated  by  a  steam  coil  to  50°  to  60°  C. 
and  electrolyzed  with  such  a  high  current  density  that  there  is 
a  violent  evolution  of  gas.  Copper  plating  is  used  not  only  as 
a  preliminary  coating  for  other  metals,  but  largely  also  for  a 
final  ornamental  covering  for  iron.  Various  colors  are  then 
produced  on  the  copper  by  dipping  into  a  bath  of  sodium  sul- 
phide, producing  the  so-called  oxidized  copper. 

Zinc  Plating 

A  zinc  covering  is  very  useful  as  a  protection  for  iron.  It 
has  the  advantage  over  tin  for  this  purpose  that  it  is  more 
electropositive  than  iron,  so  that  in  case  a  part  of  the  iron 
becomes  exposed  and  wet,  zinc  tends  to  dissolve  in  place  of  the 
iron.  Iron  is  covered  with  zinc  by  the  two  methods  of  electro- 
plating and  of  dipping  in  a  bath  of  melted  zinc.  A  third  method, 
called  sherardizing,  consists  in  heating  objects  in  zinc  dust  to 
300°  C.1  The  zinc  deposited  electrolytically  is  not  so  bright 
and  pleasing  in  appearance  as  the  dipped  zinc,  but  it  has 
been  shown  to  protect  the  iron  much  more  thoroughly.2  A 
good  solution  for  zinc  plating  is  200  grams  of  zinc  sulphate, 
ZnSO4  •  7  H2O,  40  grams  of  sodium  sulphate,  Na2SO4  - 10  H2O, 
and  10  grams  of  zinc  chloride  per  liter,  slightly  acidified  with 
sulphuric  acid.  The  current  density  is  from  ^  to  2  amperes  per 

8  Haber,  Grundriss  der  technischen  Electrochem.  p.  283. 

1  Electrochein.  and  Met.  Ind.  5,  187,  (1907). 

8  Burgess,  Electrochem.  and  Met.  Ind.  3,  17,  (1905). 


ELECTROPLATING  AND  ELECTROTYPING        37 

square  decimeter.3  The  anodes  are  of  zinc.  Since  a  little 
more  zinc  dissolves  than  is  deposited,  the  solution  would  lose 
its  acidity  unless  a  small  amount  of  sulphuric  acid  is  added  as 
it  is  used  up.  The  resistance  may  be  reduced  by  warming  to 
40°  or  45°  C. 

Brass  Plating 

In  order  to  cause  copper  and  zinc  to  deposit  simultaneously, 
it  is  necessary  that  the  metals  should  be  dissolved  in  a  solution 
in  which  a  zinc  and  a  copper  plate  would  have  potentials  nearly 
equal.  This  is  the  case  in  a  cyanide  solution.  By  replacing 
half  of  the  copper  cyanide  in  the  bath  given  above  by  zinc  cya- 
nide, a  suitable  bath  for  brass  plating  is  obtained.  Brass  anodes 
are  used.  If  a  current  density  of  only  0.1  ampere  per  square 
decimeter  is  used,  only  a  small  amount  of  zinc  is  deposited  with 
the  copper  ;  with  0.3  ampere  per  square  decimeter,  however,  the 
deposit  contains  only  80  per  cent  of  copper.  Increasing  the 
current  density  changes  the  composition  of  the  brass  only 
slightly,  though  the  color  becomes  greenish.1 

There  is  quite  a  large  resistance  to  be  overcome  in  deposit- 
ing both  copper  and  zinc  from  their  cyanide  solutions,  as  meas- 
ured by  the  potential  difference  that  must  be  produced  between 
the  solution  and  the  cathode.  This  potential  difference  is 
found  to  be  greater  than  the  potential  of  the  metal  dipping 
into  its  cyanide  solution  when  no  current  is  flowing,  and  this 
resistance  increases  with  the  current  density,  so  that  the  poten- 
tial is  soon  reached  at  which  hydrogen  is  deposited  on  the  cop- 
per or  zinc  cathode,  in  place  of  the  metal.2 

Zinc  and  copper  are  deposited  together  from  a  solution  of 
zinc  and  copper  cyanides  considerably  below  the  potential  of  a 
pure  zinc  electrode,  which  shows  electrolytic  brass  is  an  alloy 
and  not  a  mixture  of  particles  of  pure  copper  and  pure  zinc.2 

8  Foerster,  Elektrochemie  wasseriger  Lbsungen,  p.  255. 

1  Foerster,  I.e.  p.  253. 

2  Spitzer,  Z.  f.  Elektroch.  11,  367,  (1905). 


38  APPLIED   ELECTROCHEMISTRY 

Silver  Plating 

The  double  cyanide  of  potassium  and  silver  is  universally 
used  for  silver  plating,  because  of  the  smooth  deposit  obtained 
from  this  solution.  As  stated  in  Chapter  I,  silver  is  deposited 
from  a  nitrate  solution  in  a  granular  form  entirely  unsuited  for 
plating.  A  solution  containing  from  1  to  5  per  cent  silver, 
as  potassium  silver  cyanide,  KAg(CN)2  with  |  per  cent  of  free 
potassium  cyanide,  has  been  found  satisfactory.1  Too  little  or 
too  much  free  cyanide  causes  a  bad  color  in  the  deposit.  The 
anodes  are  silver,  and  the  current  density  on  the  cathode  is 
from  0.15  to  0.5  ampere  per  square  decimeter.  Silver  is  de- 
posited only  on  a  copper  surface.  Other  metals  than  copper 
or  copper  alloys  which  are  to  be  silver  plated  are  first  copper 
plated.  In  order  to  make  the  silver  adhere  to  this  surface  it 
must  be  amalgamated  before  plating.  This  is  accomplished  by 
dipping  into  a  quicking  bath,  consisting  of  a  solution  of  30 
grams  of  the  double  cyanide  of  potassium  and  mercury, 
K2Hg(CN)4,  and  30  grams  of  potassium  cyanide,  in  one  liter 
of  water.  Articles  are  washed  after  quicking  and  placed  im- 
mediately in  the  silver-plating  bath. 

Grold  Plating 

The  solution  used  for  gold  plating  consists  of  the  double 
cyanide  of  gold  and  potassium,  KAu(CN)2.  This  can  be  pre- 
pared by  precipitating  gold  with  ammonia  in  the  form  of  ful- 
minating gold,  AuNH  •  NH2  +  3  H2O,  from  a  solution  of  gold 
chloride.  This  is  washed  and  dissolved  in  potassium  cyanide, 
and  the  ammonia  boiled  off.  The  concentration  of  gold  varies 
between  0.35  and  1  per  cent  of  gold,  with  twice  as  much  potas- 
sium cyanide.1  The  anodes  are  of  gold,  and  the  current  density 
on  the  cathode  is  about  0.2  ampere  per  square  decimeter.  Gold 
plating  is  carried  out  in  both  hot  and  cold  baths.  The  metal 
deposited  from  a  hot  solution  is  more  dense,  uniform,  and  of  a 
richer  color. 

i  Haber,  I.e.  p.  284. 
i  Haber,  I.e.  p.  287. 


ELECTROPLATING  AND  ELECTROTYPING  39 

2.   GALVANOPLASTY 

Galvanoplasty,  or  the  art  of  reproducing  the  forms  of  objects 
by  electrodeposition,  was  discovered  by  Jacoby  of  Petersburg 
in  1838.  It  is  now  used  extensively  for  electrotyping  and  the 
production  of  copper  tubes  and  of  parabolic  mirrors. 

Electrotyping 

The  first  operation  in  making  an  exact  duplicate  of  type  set 
up  ready  for  printing  is  to  take  an  impression  of  the  type  in 
wax.  The  wax  sometimes  used  is  ozokerite.  The  thickness  of 
the  sheet  of  wax  used  for  the  purpose  is  about  half  an  inch. 
After  this  has  been  carefully  inspected  to  see  that  every  letter 
is  perfect,  fine  graphite  powder  is  well  worked  into  the  surface 
by  soft  brushes.  This  is  done  in  several  operations,  by  machines 
and  by  hand.  Copper  sulphate  is  then  poured  over  the  surface 
and  iron  powder  sprinkled  over  it  to  produce  a  thin  layer  of 
copper,  which  will  make  the  whole  surface  more  conducting  than 
the  graphite  could  do.  This  is  an  example  of  the  use  of  plating 
by  contact,  explained  above.  The  sheet  is  then  hung  in  an  acid 
copper  sulphate  bath  and  electrolyzed  for  an  hour  and  a  half. 
It  is  then  removed  from  the  tank,  and  the  wax  is  warmed  and 
separated  from  the  thin  copper  sheet.  The  copper  is  next  backed 
to  give  it  mechanical  strength  by  pouring  on  it  an  alloy  of  lead 
and  antimony.  The  subsequent  purely  mechanical  operations 
of  making  the  sheet  perfectly  level,  so  that  each  letter  will  print, 
and  of  mounting  them  on  wood  need  not  be  described  in  this 
place.  The  advantages  of  electrotyping  are  the  saving  of  wear 
on  the  type,  and  the  fact  that  a  small  stock  of  type  will  prepare 
unlimited  number  of  pages ;  for  when  once  a  page  is  electro- 
typed,  the  type  used  for  preparing  this  page  may  be  used  over 
again  for  another.  Nearly  all  books  are  now  printed  in  this 
way. 


40 


APPLIED   ELECTROCHEMISTRY 


Copper  Tubes,1  Foil,  and  Wire 

Tubes  are  produced  by  depositing  copper  evenly  on  a  cylin- 
drical cathode,  and  the  copper  is  removed  when  it  has  become 
sufficiently  thick.  In  order  to  keep  the  outer  surface  of  the 

tube  smooth,  it  must  be  pol- 
ished during  the  electrolysis; 
this  is  done  in  the  Elmore2 
process  by  means  of  an  agate 
wheel  whose  edge  bears  on 
the  tube,  as  shown  in  Figure 
16.  The  wheel  turns  on  its 
axis  and  polishes  the  surface 
over  which  it  travels.  In 
the  process  of  the  Societe 
des  Cuivres  de  France,  the 
polishing  is  obtained  by 
allowing  two  tubes  to  rotate 


FIG.  16. 


Agate  wheel  for  polishing  tubes 
during  electrolysis 


in  contact  with  each  other. 
Polishing  not  only  keeps  the  surface  smooth,  but  also  makes 
the  use  of  higher  current  densities  possible. 

The  tubes  made  by  the  Elmore  process  are  usually  3  meters 
long  and  vary  up  to  1.6  meters  in  diameter.3  In  order  to  sepa- 
rate the  finished  tube  from  the  axle,  the  surface  of  the  axle 
must  be  specially  prepared  so  as  to  conduct  and  yet  not  make 
the  contact  with  the  copper  deposited  too  intimate.  This  may 
be  done  by  slightly  oxidizing  the  metal  on  which  the  copper  is 
precipitated.  The  tube  can  then  be  worked  loose  by  pressure. 

Numerous  patents  have  been  taken  out  for  the  production  of 
copper  wire,  but  only  those  would  be  of  special  interest  which 
have  proved  their  value  in  actual  use.  It  is  not  apparent,  how- 
ever, from  an  examination  of  the  literature  that  any  electrolytic 
process  for  making  copper  wire  is  in  actual  use,  and  the  same 


1  See  Pfannhauser,  Die  Herstellung  von  Metallgegenstanden  auf  Elektro- 
lytischem  Wege,  Engelhardt  Monographs,  Vol.  6,  (1903). 

2  Electrochemist  and  Metallurgist,  3,  151,  (1903). 
»  Pfannhauser,  I.e.  p.  109. 


ELECTROPLATING   AND   ELECTRO-TYPING  41 

is  true  in  the  case  of  metal  foils.  Nevertheless  a  few  of  the  best 
known  patents  will  be  described. 

In  1891,  J.  W.  Swan  patented  a  method  of  producing  copper 
wire,  which  consists  in  depositing  copper  on  a  wire  so  as  to 
thicken  it,  and  in  then  drawing  down  the  wire  to  the  original 
size.  The  apparatus  is  so  planned  that  this  is  a  continuous 
process.  Saunders  has  patented  a  method  in  which  the  copper 
is  deposited  on  a  conducting  spiral  wound  on  a  drum.  The 
wire  is  stripped  off  when  sufficiently  thick,  and  is  then  drawn 
down. 

For  the  production  of  metal  foil,  Reinfeld's  patent  calls  for 
an  oxidized  nickel  cathode.  When  a  thin  deposit  of  metal  has 
formed,  it  can  be  stripped  off.  The  principle  of  Endruweit's 
method  is  the  same.  The  cathode  is  a  metal  ribbon  which  passes 
through  an  oxidizing  solution,  then  through  a  bath  for  clean- 
ing, after  which  the  metal  foil  is  deposited  upon  it. 

Besides  the  production  of  tubes  the  only  other  galvanoplastic 
industry  which  is  of  importance  is  the  production  of  parabolic 
mirrors.4  This  process  has  been  worked  out  by  Sherard  Cow- 
per- Coles.  It  saves  the  expensive  grinding  of  a  parabolic  surface 
for  each  mirror,  for  by  this  method  any  number  of  parabolic  mir- 
rors can  be  produced  from  one  mold.  The  details  of  the  pro- 
cess are  the  following :  First  a  perfectly  parabolic  glass  surface 
is  prepared  by  pressing  a  glass  plate  about  3  centimeters  thick, 
and  hot  enough  to  be  soft,  into  a  cast-iron  mold  of  approxi- 
mately a  parabolic  form.  The  glass  surface  which  was  next 
the  iron  is  now  made  perfectly  parabolic  by  polishing  on  a 
lathe  with  more  refined  means  as  the  surface  approaches  nearer 
to  perfection.  The  next  step  is  to  clean  the  surface  and  cover 
it  with  a  thin  layer  of  metallic  silver  by  the  ordinary  process 
used  in  silvering.  The  glass  form,  covered  on  the  parabolic 
side  with  silver,  is  then  placed  in  a  copper  sulphate  bath,  ro- 
tated at  the  rate  of  five  times  a  minute,  and  copper  plated. 
The  object  of  the  copper  is  to  give  the  mirror  mechanical 
strength.  In  order  to  separate  the  silver  and  copper  from  the 
glass,  they  are  placed  in  a  water  bath  and  heated  to  50°  C. 

4  See  Coles,  Engelhardt  Monographs,  Vol.  14,  (1904). 


42  APPLIED   ELECTROCHEMISTRY 

The  unequal  expansion  easily  separates  the  glass  from  the 
metal.  The  concave  side  is  now  a  perfect  mirror,  but  the 
silver  would  soon  tarnish  and  must  therefore  be  protected. 
For  this  purpose  a  thin  layer  of  platinum  is  deposited  on  the 
silver  electrolytically.  The  solution  used  for  platinizing  is 
ammonium  platinic  chloride  in  sodium  citrate.  The  only  pro- 
cess that  now  remains  to  make  the  mirror  complete  is  its 
mounting,  the  description  of  which  in  this  place  is  unnecessary. 


CHAPTER   IV 

ELECTROLYTIC  WINNING  AND  REFINING  OP  METALS  IN 
AQUEOUS  SOLUTIONS 

1.    THE  WINNING  OF  METALS 

ATTEMPTS  have  been  made  to  extract  metals  from  their  ores 
by  electrolyzing  the  ore  as  an  anode,  in  the  hope  that  it  would 
dissolve  and  be  deposited  at  the  cathode  in  the  pure  state.  No 
such  process  has  ever  been  successful,  but  as  failures  are  in- 
structive, the  three  best  known  processes  for  the  electrolytic 
winning  of  metals  will  be  briefly  described. 

An  attempt  to  put  the  Marchese  process  in  operation  is 
described  by  Cohen.1  The  matte  from  which  the  copper  was 
to  be  won  had  the  following  composition: 

Copper 17.20  per  cent 

Lead 23.70  per  cent 

Iron 29.18  per  cent 

Sulphur 21.03  per  cent 

SO3 0.69  percent 

Silica 0.88  per  cent 

Silver 0.062  per  cent 

The  solution  was  obtained  by  treating  a  matte  similar  to  the 
above  with  dilute  sulphuric  acid,  and  consisted  principally  of 
copper  and  ferrous  sulphate.  On  electrolyzing,  copper  de- 
posits on  the  cathode  and  copper  and  iron  are  dissolved  at  the 
anode  as  sulphates.  In  order  to  make  the  oxidizing  power  of 
ferric  sulphate  available,  the  matte  from  which  the  solution  is 

i  Z.  f.  Elektroch.  1,  50,  (1894). 
43 


44  APPLIED   ELECTROCHEMISTRY 

made  is  treated  with  the  electrolyte  in  which  ferric  sulphate 
has  accumulated.  The  ferric  sulphate  is  reduced  to  ferrous 
sulphate,  and  cuprous  sulphide  and  oxide  is  changed  to  copper 
sulphate.  The  solution  is  then  returned  to  the  electrolyzing 
baths. 

Favorable  results  were  obtained  in  the  laboratory  in  Genoa, 
and  on  a  larger  scale  at  Stolberg  from  February  to  April,  1885. 
The  copper  obtained  was  99.92  per  cent  pure.  A  large  plant 
was  then  built  to  produce  500  to  600  kilograms  of  copper  in  24 
hours  with  58  vats,  2.2  meters  long,  1  meter  deep,  and  1  meter 
wide.  At  first  all  expectations  were  realized.  The  baths 
worked  well  and  the  copper  produced  was  pure.  Within  a  few 
days,  however,  the  voltage  across  the  baths  began  to  rise,  in 
some  cases  to  5  volts.  This  was  due  to  the  deposition  of  sul- 
phur on  the  anode  and  the  disintegration  of  the  anode  due  to 
the  dissolving  of  the  copper  and  iron.  Large  pieces  became 
detached  from  the  anode  and  fell  to  the  bottom  of  the  tank, 
filling  up  the  space  between  anode  and  cathode  and  producing 
a  short  circuit.  The  copper  also  became  impure,  containing 
antimony,  bismuth,  lead,  iron,  zinc,  and  sulphur.  Insoluble 
lead  electrodes  were  then  tried,  but  the  polarization  due  to  the 
formation  of  lead  peroxide  was  excessive,  and  the  yield  in  cop- 
per fell  to  60  per  cent  of  the  theoretical  amount.  The  Siemens 
and  Halske  process  was  then  tried  by  the  same  company.  The 
principal  difference  between  this  and  the  Marchese  process  is 
the  use  of  insoluble  anodes  and  the  separation  of  anode  and 
cathode  by  a  diaphragm.  Copper  is  deposited  from  a  solution 
containing  ferrous  sulphate  and  copper  sulphate.  The  solution 
then  circulates  to  the  anode,  where  ferrous  sulphate  is  oxidized 
to  the  ferric  state.  The  oxidized  solution  is  then  used  to  dis- 
solve more  copper  from  the  ore.  For  three  months  an  attempt 
was  made  to  carry  out  this  process,  but  it  was  finally  given  up, 
partly  at  least  on  account  of  mechanical  difficulties,  such  as  the 
tearing  of  the  diaphragm  and  disintegration  of  the  carbon 
anodes. 

The  Hoepf ner 2  process  is  similar  in  principle  to  the  Siemens 

2  Z.  f.  angew.  Ch.  p.  160,  (1891);  Chem.  Zeitung  p.  1906,  (1894). 


REFINING   OF   METALS    IN   AQUEOUS   SOLUTIONS  45 

and  Halske  process.  The  unroasted  ore  is  dissolved  by  cupric 
chloride,  and  the  cupric  chloride  is  reduced  to  cuprous  chloride. 
This  is  kept  in  solution  by  sodium  chloride.  The  action  of  the 
cupric  chloride  is  the  following  : 3 

Cu2S  +  2  CuCl2  =  4  CuCl  +  S. 

The  solution  containing  cuprous  chloride  is  electrolyzed  in 
the  cathode  compartment,  where  it  loses  part  of  its  copper.  The 
solution  then  circulates  to  the  anode  compartment,  from  which 
the  cathode  compartment  is  separated  by  a  diaphragm,  arid  the 
remaining  copper  is  oxidized  to  cupric  chloride.  The  anode 
solution  is  then  ready  for  treating  the  ore  a  second  time.  This 
process  was  also  tried  on  a  large  scale,  but  seems  to  have  failed 
largely  on  account  of  mechanical  difficulties,  especially  with  the 
diaphragm. 

The  Winning  of  Zinc 

Zinc  is  one  of  the  few  metals  in  the  winning  of  which  elec- 
trolysis may  take  an  important  part.  This  is  due  to  the  fact 
that  in  the  ordinary  metallurgical  process  a  loss  amounting 
sometimes  to  25  per  cent  of  the  metal  occurs.1  Only  under 
peculiar  circumstances  is  zinc  refined  by  electrolysis,  on  account 
of  the  fact  that  commercial  zinc  never  contains  noble  metals, 
and  also  because  there  is  not  much  demand  for  zinc  of  a  high 
degree  of  purity.2 

In  either  a  refining  or  a  winning  process  it  is  of  the  first 
importance  to  find  the  conditions  under  which  a  smooth  deposit 
of  the  metal  can  be  obtained. 

Under  certain  conditions  zinc  is  deposited  in  a  spongy  form 
that  cannot  be  melted  down  on  account  of  its  tendency  to 
oxidize.3  The  nature  of  sponge  zinc  is  still  unknown,4  though 
the  conditions  under  which  it  forms  and  the  ways  to  avoid  it 

8  See  Blount,  Practical  Electrochemistry,  p.  81,  footnote. 

1  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  289. 

2  Giinther,  Die  Darstellung  des  Zinks,  p.  26. 

8  Mylius  and  Fromm,  Z.  f.  anorg.  Ch.  9,  144,  (1895). 
4  Foerster,  I.e.  p.  291. 


46  APPLIED   ELECTROCHEMISTRY 

have  been  the  subject  of  numerous  investigations.  The  factors 
which  determine  the  character  of  the  deposit  are  the  tempera- 
ture, the  current  density,  the  concentration  of  the  solution,  and 
the  impurities  present. 

From  a  dilute  solution  of  zinc  sulphate,  the  zinc  is  always 
deposited  in  a  spongy  state6  with  a  simultaneous  evolution  of 
hydrogen.  With  a  low  current  density  even  in  a  strong  solu- 
tion the  same  is  true.  High  temperature,6  oxidizing  agents, 
and  metals  more  electronegative  than  zinc7  cause  the  forma- 
tion of  sponge.  A  slight  acidity  tends  to  prevent  the  sponge 
from  forming.8  Therefore  the  conditions  to  obtain  zinc  in  a 
compact  form  are  high  current  density,  low  temperature,  a  con- 
centrated, slightly  acid  solution,  and  the  absence  from  the  solu- 
tion of  oxidizing  agents  or  more  electronegative  metals  than 
zinc.  As  to  the  limits  of  current  density  allowable,  different 
results  have  been  obtained  by  different  observers.  According 
to  Mylius  and  Fromm,9  the  current  density  must  be  at  least 
one  ampere  per  square  decimeter  to  prevent  the  formation  of 
spongy  zinc,  while  Hasse 10  obtained  solid  deposits  with  one 
third  this  density.  The  strength  of  the  solution  is  not  given. 
Kiliani's11  deposits  were  spongy  at  a  current  density  of  2.7  am- 
peres per  square  decimeter,  from  a  zinc  sulphate  solution  of 
specific  gravity  1.38.  Nahnsen  seems  to  have  investigated  the 
condition  of  deposit  with  regard  to  temperature  and  current 
density  more  systematically  than  any  one  else.  He  obtained 
the  following  results : 

6  Kiliani,  Berg-  und  Huttenm.  Ztg.,  1883,  p.  250. 

6  Nahnsen,  Berg- und  Huttenm.  Ztg.  1891,  p.  393. 

7  Mylius  and  Fromm,  I.e.  p.  165. 

8  Mylius  and  Fromm,  I.e.  p.  167. 

9  Mylius  and  Fromm,  I.e.  p.  169. 

10  Z.  f.  Berg-,  Htittenm-  und  Salinenwesen,  45,  327,  (1897). 

11  Kiliani,  I.e.  p.  251. 


REFINING   OF  METALS   IN   AQUEOUS   SOLUTIONS 
TABLE  5 


47 


AMP.  PER  SQ.  METER 

0° 

10° 

20° 

80° 

10 
50 

Firm 
Firm 

Incipient 
sponginess 
Spongy 

Spongy 
Incipient 

Spongy 
Spongy 

100 

Firm 

Firm 

sponginess 
Spongy 

Incipient 

150 

200 

Firm 
Firm 

Firm 
Firm 

Firm 
Firm 

sponginess 
Spongy 
Firm 

In  the  winning  of  zinc  by  electrolysis,  the  steps  are  to  roast 
the  ore  if  it  is  insoluble,  to  dissolve  the  resulting  product,  and 
to  deposit  the  zinc  from  the  solution  by  electrolysis  with  in- 
soluble anodes.  A  process  devised  by  Hoepfner  to  carry  out 
the  winning  of  zinc  in  this  way  was  in  operation  for  a  while  in 
Fiirfurth,  Germany,  and  is  now  in  operation  in  Hruschau, 
Austria,  and  at  the  works  of  Brunner,  Mond,  and  Company, 
at  Winnington,  England.12  The  process  consists  in  electrolyz- 
ing  zinc  chloride  with  carbon  anodes,  separated  by  a  diaphragm 
from  the  cathode.13  One  great  difficulty  is  to  obtain  a 
diaphragm  that  will  last,  and  it  seems  doubtful  if  this  problem 
has  yet  been  satisfactorily  solved.  The  chlorine  obtained 
from  the  anode  compartments  is  collected  and  used  in  making 
bleaching  powder.1* 

2.   THE  ELECTROLYTIC  REFINING  OF  METALS 
Copper  Refining 

The  object  of  copper  refining  is  to  get  as  pure  a  copper  as 
possible  for  electric  conductors,  since  a  very  small  amount  of 
impurity  lowers  the  conductivity  materially,1  and  also  to  ob- 
tain the  gold,  silver,  and  other  impurities. 

12  Kershaw,  Electrometallurgy,  p.  272. 

18  For  a  detailed  description  see  GUnther,  I.e. 

14  Kershaw,  I.e.  p.  273.  *  Addicks,  Electrochem.  Ind.  1,  580,  (1903). 


48  APPLIED   ELECTROCHEMISTRY 

In  copper  refining,  copper  anodes  containing  only  a  small 
percentage  of  impurities  are  electrolyzed  with  the  proper 
current  density  in  an  acid  copper  sulphate  bath  of  suitable 
concentration.  The  copper  and  the  soluble  impurities,  which 
are  not  more  electronegative  than  copper,  dissolve,  while  the 
insoluble  impurities  become  detached  from  the  anode  and  fall 
to  the  bottom  of  the  tank,  forming  what  is  known  as  anode 
mud  or  slime.  The  soluble  impurities  gradually  accumulate 
in  the  solution  till  purification  is  necessary.  As  long  as  the 
impurities  are  below  a  certain  concentration  in  the  solution,  the 
copper  deposited  on  the  cathode  is  of  much  greater  purity  than 
that  of  the  anode.  The  reason  the  impurities  in  solution  are 
not  deposited  when  dilute  is  that  the  voltage  drop  from  solu- 
tion to  cathode  has  not  reached  the  decomposition  point  of 
these  ions.  The  decomposition  point  of  an  ion  changes  with 

its  concentration  by  the  amount  — ' volt  at  17°  C.,  where  n 

n 

the  valence  of  the  metal,  for  a  change  in  concentration  of  the 
ion  in  the  ratio  of  one  to  ten.  As  the  concentration  of  any 
given  ion  increases,  its  decomposition  point  is  gradually  lowered 
until  it  equals  the  potential  difference  between  the  solution  and 
the  cathode.  At  this  point  it  is  deposited  with  the  copper. 
But  not  all  of  the  impurities  found  in  the  cathode  are  deposited 
from  the  solution.  Some  are  taken  up  from  the  slime,  of  which 
a  certain  amount  is  always  suspended  in  the  solution,  on  account 
of  the  circulation  of  the  electrolyte.  This  is  true  in  the  case 
of  silver  and  gold.2 

It  will  be  interesting  next  to  see  what  the  impurities  of 
anode  copper  commonly  are,  how  they  behave  when  the  anode 
dissolves,  and  what  impurities  are  deposited  on  the  cathode. 
The  following  table  gives  a  representative  composition  of 
anodes  for  American  refineries  : 

Copper 98-99.5  per  cent 

Silver 0  to  300  oz.  per  ton 

Gold 0  to  40  oz.  per  ton 

Arsenic 0  to  2  per  cent 

2  Addicks,  Electrochem.  and  Met.  Ind.  4,  16,  (1906). 


REFINING   OF  METALS    IN   AQUEOUS    SOLUTIONS 


49 


with  small  amounts  of  antimony,  bismuth,  iron,  nickel,  sulphur, 
selenium,  tellurium,  and  silicon. 

A  more  specific  case  is  given  in  the  following  tables,  showing 
the  composition  of  the  anodes  and  cathodes  at  the  Great  Falls 
and  the  Anaconda  refineries.3 

COMPOSITION  OF  ANODES  IN  PER  CENT 


GREAT  FALLS 

ANACONDA 

Copper                    .                

99  27 

99  25 

Arsenic  and  antimony                                         . 

0  07 

0  10 

61.40 

90.00 

Oz.  gold  per  ton    

0.22 

0.50 

For  comparison  the  cathodes  are  given  below. 

COMPOSITION  OF  CATHODES  IN  PER  CENT 


GREAT  FALLS 

ANACONDA 

Copper                                                                  . 

99.95 

99.96 

Arsenic 

0  0012 

0  0009 

0.0033 

0.0023 

Oz.  silver  per  ton       

1.0 

0.25 

The  behavior  of  these  impurities  in  the  anode  under  the 
action  of  the  current  was  first  determined  by  Kiliani.4  His 
experiments  were  carried  out  with  a  constant  current  density 
on  the  anode  of  20  amperes  per  square  meter  and  with  a  solu- 
tion of  150  grams  of  copper  sulphate  and  50  grams  of  concen- 
trated sulphuric  acid  per  liter.  His  results  will  be  briefly 
recapitulated.  Excepting  the  above  statement  regarding  cur- 
rent density  and  concentrations,  his  method  of  experimenting 
is  not  indicated. 

Cuprous  oxide  is  not  attacked  by  the  current,  but  goes  into 
the  slime,  where  it  is  slowly  dissolved,  making  the  bath  richer 
in  copper  and  poor  in  sulphuric  acid. 

8  H.  O.  Hofman,  Electrochem.  Ind.  1,  416,  (1903). 

4  Berg-  und  Huttenm.  Ztg.  1885,  pp.  249,  261,  and  273. 


50  APPLIED   ELECTROCHEMISTRY 

Copper  sulphide  and  selenium  sulphide  go  into  the  slime. 

Silver,  gold,  and  platinum  go  into  the  slime. 

Bismuth  and  bismuth  oxide  go  partly  into  the  slime  and 
partly  into  solution,  from  which  they  are  precipitated  as  a  basic 
salt. 

Tin  goes  into  solution  and  precipitates,  on  standing,  as  basic 
salt. 

Metallic  arsenic  goes  into  solution  as  arsenic  acid.  If  pres- 
ent to  less  than  one  per  cent  in  the  anode,  it  goes  more  rapidly 
into  the  slime.2 

Antimony  behaves  like  tin. 

Lead  goes  into  the  slime  as  insoluble  sulphate. 

Iron,  zinc,  nickel,  and  cobalt  are  dissolved  by  the  current 
and  remain  in  solution. 

A  common  composition  of  the  slime  is  the  following:2 

40  per  cent  silver, 

2  per  cent  gold, 
25  per  cent  copper, 

5  per  cent  selenium  and  tellurium, 
10  per  cent  arsenic  and  antimony, 
18  per  cent  lead,  silicon,  sulphuric  acid,  etc. 

The  slimes  at  Great  Falls  and  Anaconda  are  the  following  : 3 


GBEAT  FALLS 

ANACONDA 

18  per  cent  copper 
15,000  oz.  of  silver  per  ton 
38  oz.  of  gold  per  ton 

10  per  cent  copper 
18,000  oz.  of  silver  per  ton 
100  oz.  of  gold  per  ton 

The  large  amount  of  copper  in  the  slime  is  due  to  part  of  the 
dissolving  in  the  cuprous  state  and  then  breaking  up  into 
cupric  ions  and  finally  divided  copper  according  to  the 
equation  : 

2  Cu+  =  Cu++  +  Cu.5 

The  slimes  are  worked  up  for  the  gold,  silver,  copper,  and 
arsenic.  The  gold  and  silver  have  to  be  purified,  and  for  this 

*  Foerster,  Z.  f.  Elektroch.  3,  497,  (1907)  ;   Wohlwill,  ibid.  9,  311,  (1903). 


REFINING   OF   METALS    IN   AQUEOUS   SOLUTIONS 


51 


reason    copper   refineries   sometimes   have   a   plant   for   silver 
refining.6 

The  electrolyte  used  in  copper  refining  consists  of  a  solution 
of  copper  sulphate  and  sulphuric  acid.  The  quantity  of  cop- 
per sulphate  (CuSO4  +  5  H2O)  varies  between  12  and  20  per 
cent,  the  acid  between  4  and  7  per  cent.7  Table  6  gives  the 
conductivities  per  centimeter  cube  of  two  acid  copper  sulphate 
solutions,  one  containing  approximately  the  smallest  amounts 
of  salts  and  acid  used,  and  the  other,  the  largest  amounts.8 

TABLE  6 


TEMP.  CENTIGRADE 

CONDUCTANCE  OF  A  SOLUTION  CONTAINING 

3.75%  H2S04 
12.5%  CuS04  •  5  H,0 
Spc.  gr.  at  22.2,  1.007 

9.2%  H,S04 
18.3%CuS04-5H20 
Spc.gr.  at  21.2,  1.199 

25 
40 
60 

0.1573 
0.1752 
0.1895 

0.3260 

0.3754 
0.4252 

This  shows  the  limits  between  which  the  conductance  of  a 
copper  sulphate  solution  used  in  copper  refining  would  proba- 
bly lie.  The  actual  composition  of  the  baths  at  Great  Falls 
and  Anaconda  are  the  following  : 


GREAT  FALLS 


ANACONDA 


150  grams  sulphuric  acid  per  liter 
40  grams  copper  per  liter 


170  grains  sulphuric  acid  per  liter 
42  grams  copper  per  liter 


A  small  amount  of  hydrochloric  acid  is  also  added  to  prevent 
the  solution  of  silver  and  antimony,  as  well  as  to  produce  a 
smoother  deposit  on  the  cathode.  Where  a  current  density  as 
low  as  ten  amperes  per  square  foot  is  employed,  as  at  Anaconda, 

6  Easterbrooks,  Silver  Refining  Plant  of  the  Raritan  Copper  Works,  Electro- 
chem.  and  Met.  Ind.  6,  277,  (1908). 

7  Ulke,  Die  Elektrolytische  Raffination  des  Kupfers,  p.  42,  (1904). 

8  Thompson  and  Hamilton,  Trans.  Am.  Electroch.  Soc.  17,  292,  (1910). 


52 


APPLIED   ELECTROCHEMISTRY 


the  electrolyte  can  be  used  for  many  years  without  purification,9 
while  with  a  60  per  cent  higher  value  some  part  must  be  re- 
newed frequently.  A  foul  solution  at  Great  Falls  has  the  fol- 
lowing composition  :  3 

51.80  grams  copper  per  liter, 
13.20  grains  iron  per  liter, 
14.00  grams  arsenic  per  liter, 

0.62  grams  antimony  per  liter, 
48.00  grams  sulphuric  acid  per  liter. 

This  shows  that  the  impurities  can  become  fairly  concentrated 
before  purification  is  necessary. 

In  those  refineries  where  the  electrolyte  has  to  be  purified, 
the  operation  of  purifying  is  carried  out  continuously  on  a  cer- 
tain fraction  of  the  total  amount  of  electrolyte.  The  copper  is 
separated  either  by  electrolyzing  with  lead  anodes  or  by  crys- 
tallizing as  copper  sulphate. 

The  circulation  of  the  electrolyte,  which  is  maintained  by 
arranging  the  vats  as  in  Figure  17,  is  an  important  factor. 
With  no  circulation  the  solution  at  the  cathode  would  become 


1  --EL 

-  :  -'-•-'    "  -^""     ~  ~~  ""*"*  ^-1-"-!  ?  J 


FIG.  17.  —  Circulation  of  electrolyte 

too  dilute  for  satisfactory  deposition,  while  with  too  much  cir- 
culation the  slime  would  be  stirred  up  and  contaminate  the 
cathode.  The  higher  the  current  density  the  higher  must  be 
the  rate  of  circulation.  This  is  illustrated  by  the  fact  that 
at  Great  Falls,  with  tanks  9J  feet  in  length,  2J  feet  in  width, 
and  3|  feet  in  depth,  where  the  current  density  is  about  40  am- 
peres per  square  foot,  the  circulation  through  a  tank  is  6  gal- 

9  Magnus,  Trans.  Am.  Electrochem.  Soc.  4,  77,  (1903). 


KEFINING   OF   METALS    IN   AQUEOUS    SOLUTIONS 


53 


B 


Ions  per  minute;  while  at  Anaconda,  with  tanks  8J  feet  in 
length,  4  feet  in  width,  and  4  feet  in  depth  and  a  current 
density  of  10  amperes  per  square  foot,  the  circulation  is  3 
gallons  per  minute.3  At  the  Raritan  Copper  Works  the  rate 
of  circulation  would  empty  a  tank  in  1|  hours.10 

There  are  two  different  systems  of  arranging  the  electrodes 
used  in  refining  copper,  known  as  the  series  and  the  multiple 
systems.  In  the  se- 
ries system  a  num- 
ber of  copper  anodes 
are  suspended  in 
the  bath  at  equal 
distances  apart,  and 
only  the  two  end 
ones  are  connected 
to  the  dynamo,  as 
shown  in  Figure  18. 
The  current  then  dissolves  copper  from  the  first  plate,  which  is 
connected  directly  to  the  opposite  pole  of  the  dynamo,  and 
deposits  it  on  the  near  side  of  the  next  plate.  The  other  side 

of  the  second  plate 

—         c        c        c        c        c 


+ 

C 

0 

E 

F 

C 

i 



*  ~ 

// 

- 

J.— 

4-  "=• 

*  - 

•f   - 

+"  - 

¥  - 

~  % 

~    '// 

^ 

- 

- 

- 

-I 

—  - 

—  -_ 

—   • 

— 

n_r 

_ 

-     \ 

u. 

Tvrmrrr, 

~       •* 

—   J 

— 

- 

— 

J     -1 

j 

FIG.  18.  —  Series  system 


FIG.  19.  —  Multiple  system 


is  dissolved  and 
deposited  on  the 
third,  and  so  on 
throughout  the 
whole  series.  In 
order  to  separate 
the  deposited  cop- 
per from  that 
which  has  not  been 
dissolved,  the  sides 


facing  the  positive  pole  are  covered  with  some  conducting 
material  which  allows  the  refined  copper  to  be  stripped  off. 
Of  course  in  this  system  the  tanks  cannot  be  lined  with  con- 
ducting material,  for  such  a  lining  would  cause  a  short  circuit. 
Another  difference  between  these  tanks  and  those  of  the  multi- 


10  Addicks,  Min.  Ind.  9,  270,  (1900),  and  Ulke,  I.e.  p.  63. 


54  APPLIED   ELECTROCHEMISTRY 

pie  system  is  their  greater  size.  Those  at  the  Nichols  Works 
in  Brooklyn  are  16  feet  long,  5  feet  wide,  and  5J  feet  deep.11 
The  anodes  are  from  £  to  f  of  an  inch  thick,  and  are  placed 
from  |  to  -f$  of  an  inch  apart. 

In  the  multiple  system  the  anodes  and  cathodes  are  arranged 
alternately,  as  shown  in  Figure  19.  All  the  anodes  are  con- 
nected to  the  positive  pole  of  the  dynamo  and  the  cathodes  to 
the  negative  pole.  The  cathodes  are  thin  sheets  of  electrolytic 
copper,  made  by  depositing  copper  on  lead  or  copper  covered 
with  a  conducting  material  from  which  the  copper  can  be  sepa- 
rated. At  the  Raritan  Copper  Works  6  the  cathodes  remain  in 
the  tanks  14  days.  At  the  end  of  28  days  13  per  cent  of  the 
anodes  are  still  undissolved,  but  at  this  stage  they  are  removed 
and  cast  into  fresh  anodes. 

In  order  to  reduce  the  power  required,  the  temperature  of 
the  baths  in  practice  is  between  40°  C.  and  50°  C.,  though  from 
some  experiments  of  Bancroft12  70°  C.  and  a  current  density 
between  3.5  and  3.75  amperes  per  square  decimeter  would 
seem  to  be  more  economical  as  far  as  power  is  concerned. 

The  voltage  between  the  anode  and  cathode  varies  between 
0.1  and  0.3  volt,  depending  on  current  density,  temperature, 
distance  between  anode  and  cathode.13  This  voltage  is  used 
up  partly  in  overcoming  the  ohmic  resistance  of  the  bath  and 
partly  in  overcoming  the  electromotive  force  of  polarization. 
Polarization,  of  course,  varies  with  the  current  density  and  the 
rate  of  circulation,  but  a  representative  value  is  0.02  volt.14 

The  actual  cost  of  refining  98  per  cent  copper  has  in  recent 
years  been  reduced  from  $20  to  |4  or  |5  a  ton.  This  im- 
provement is  due  to  the  more  economical  use  of  power 15  and 
the  more  practical  handling  of  the  material.  About  24  per 
cent  of  the  power  is  still  lost  in  the  contact  resistance.16 

11  Ulke,  I.e.  p.  6  et  seq. 

12  Trans.  Am.  Electrochem.  Soc.  4,  73,  (1903). 
i*  Ulke,  I.e.  p.  43. 

14  Addicks,  Trans.  Am.  Electrochem.  Soc.  7,  62,  (1905). 

i*  Ulke,  I.e.  p.  3. 

i6  Magnus,  Electrochem.  Ind.  1,  661,  (1903). 


REFINING   OF   METALS   IN   AQUEOUS   SOLUTIONS  55 

Nickel  Refining 

If  nickel  is  deposited  from  a  cold  solution  of  nickel  chloride 
or  sulphate  in  a  layer  more  than  0.01  millimeter  thick,  it  has  a 
great  tendency  to  separate  from  the  underlying  metal,  but  this 
difficulty  can  be  overcome  by  heating  the  solution  from  which 
the  nickel  is  deposited  to  60°  or  70°. l  At  this  temperature  and 
with  a  current  density  of  from  0.01  to  0.02  ampere  per  square 
centimeter,  nickel  is  obtained  of  such  ductility  that  it  can  be 
rolled.  Nickel  is  more  electropositive  than  hydrogen,  and  the 
overvoltage  of  hydrogen  on  nickel  is  not  great.  Nickel  must 
therefore  be  deposited  from  a  very  weakly  acid  solution. 

The  Balbach  Company  at  Newark,  New  Jeresy,  was  one  of 
the  earliest  refiners  of  nickel,  as  well  as  of  copper.  Nickel  was 
refined  by  this  company  from  1894  to  1900  by  a  secret  process. 
The  product  contained  0.25  per  cent  iron  and  a  small  amount 
of  cobalt.2  Another  process  that  was  in  successful  operation 
for  some  time  is  that  of  David  H.  Brown.3  This  was  not  a  re- 
fining operation,  as  it  had  for  its  object  the  separation  of  nickel 
and  copper  in  an  ore.  The  ore  contained  2  per  cent  nickel 
and  as  much  copper.  Anodes  were  made  consisting  of  54.3 
per  cent  copper,  43.08  per  cent  nickel,  and  the  remainder  of 
iron  and  sulphur.  They  were  75  centimeters  in  width,  60  in 
length,  and  2J  in  thickness.  The  connections  were  those  of 
the  multiple  system.  The  tanks  were  of  concrete,  256  centi- 
meters long,  85  centimeters  wide,  and  67|  centimeters  deep. 
Each  held  1.534  cubic  meters  of  electrolyte.  The  circulation 
was  effected  as  in  copper  refining,  by  overflow  from  bath  to 
bath.  The  solution  at  one  time  consisted  of  44. 3  grams  of  copper 
per  liter  as  cuprous  chloride,  55.6  grams  of  nickel  as  nickel  chlo- 
ride, and  100  grams  of  sodium  chloride,  but  these  concentrations 
were  subsequently  modified.  The  voltage  for  24  baths  in  series 
was  6  to  10  volts  and  the  current  500  amperes.  In  this  stage 
copper  was  deposited  in  a  coherent  but  not  dense  form.  The 

iFoerster,  Z.  f.  Elektroch.  4, 160,  (1897). 

2  Ulke,  Electrochem.  Ind.  1,  208,  (1903). 

3  Haber,  Z.  f.  Elektroch.  9,  392,  (1903). 


56 


APPLIED   ELECTROCHEMISTRY 


relative  amount  of  copper  and  nickel  in  the  solution  flowing  into 
the  baths  was  the  same  as  that  in  the  anodes.  On  leaving  the 
baths  the  ratio  of  copper  to  nickel  was  reduced  to  1  :  80.  Sodium 
sulphide  was  then  added  to  the  solution,  to  precipitate  the  1.25  per 
cent  of  copper  still  remaining.  After  filtering,  the  solution  was 
treated  with  chlorine  to  change  the  iron  to  chloride,  which  was 
precipitated  with  sodium  hydrate  and  filtered.  As  much  as  pos- 
sible of  the  sodium  chloride  was  then  removed  by  concentrating 
the  solution  by  evaporation.  The  nickel  was  then  obtained  by 
electrolyzing  the  hot  solution  with  graphite  anodes.  The  current 
yield  was  92.5  per  cent  of  the  theoretical.  The  chlorine  pro- 
duced at  the  anode  was  used  in  another  part  of  the  process. 
The  nickel  obtained  was  of  the  following  average  composition: 
99.85  per  cent  nickel,  0.085  per  cent  iron,  0.014  per  cent 
copper,  and  was  free  from  arsenic,  sulphur,  and  silicon. 

Up  to  1902,  454  kilograms  of  nickel  were  produced  daily  in 
Cleveland,  when  it  was  discontinued  by  the  International  Nickel 
Trust,  in  favor  of  the  Orford  *  Process  with  which  it  formerly 
competed.  The  nickel  produced  by  the  latter  process  has  vary- 
ing compositions,  as  the  following  table  of  percentage  composi- 
tion shows: 


NICKEL  AND 
COBALT 

COPPER 

FLUORINE 

CARBON 

SULPHUR 

SILICON 

98.91 

0.13 

0.40 

0.23 



0.05 

98.34 

0.41 

0.93 



0.078 



This  is  pure  enough  for  anodes  in  nickel  plating  and  the 
manufacture  of  steel.  For  other  purposes,  however,  such  as 
making  German  silver,  a  better  quality  is  required,  and  since 
1906  the  Orford  Copper  Company  has  taken  up  the  electrolytic 
refining  of  nickel.6  Very  little  is  known  about  the  details  of 

4  This  process  depends  for  the  separation  on  the  fact  that  sodium  sulphide 
forms  double  compounds  with  iron  and  copper  sulphides,  which  float  on  the  top 
of  melted  nickel  sulphide. 

6  Electrochem.  and  Met.  Ind.  4,  2tf,  (1906). 


REFINING    OF   METALS    IN   AQUEOUS    SOLUTIONS  57 

this  process.  The  cathodes  are  said  to  be  3  by  4  feet  in  area 
and  |  inch  in  thickness,  and  their  purity  is  99.5  per  cent.  The 
nickel  is  deposited  from  a  chloride  solution. 

Silver  Refining 

Two  different  cases  arise  in  refining  silver :  one  being  the 
problem  of  separating  silver  and  copper  in  an  alloy  consisting 
mainly  of  these  two  metals ;  the  other,  the  separation  of  silver 
from  relatively  small  amounts  of  gold  and  platinum.  From 
the  relative  positions  of  silver  and  copper  in  the  electrolytic 
series,  it  is  evident  that  if  the  attempt  were  made  to  separate 
these  metals  by  electrolyzing  an  anode  containing  approximately 
equal  amounts  of  each  in  a  solution  which  dissolves  them  both, 
more  silver  would  deposit  on  the  cathode  than  dissolves  at  the 
anode.  The  copper  in  solution  would  therefore  become  so  con- 
centrated that  its  decomposition  point  would  be  reduced  to  a 
value  equal  to  that  of  silver.  In  carrying  out  this  operation  it 
is  therefore  necessary  either  to  find  a  solvent  in  which  only  one 
of  the  metals  dissolves,  or  to  precipitate  one  of  them  by  some 
other  means.  In  1877  to  1878  Wohlwill1  succeeded  in  separat- 
ing silver  and  copper  at  the  Norddeutsche  Amnerie  in  alloys 
containing  as  much  as  30  per  cent  of  silver.  The  solution  was 
copper  sulphate,  more  dilute  than  is  used  in  refining  copper,  and 
the  current  density  was  lower.  A  sponge  rich  in  silver  re- 
mained adhering  to  the  anode,  which  had  to  be  removed  me- 
chanically, and  the  copper  was  deposited  at  the  cathode.  Another 
method  for  accomplishing  the  same  result,  due  to  Dietzel 2  and 
used  at  the  Gold-  und  Silber-Scheide  Anstalt  at  Pforzheim,  de- 
pends on  dissolving  both  copper  and  silver  in  a  weakly  acid  solution 
of  copper  nitrate  at  the  anode  and  carrying  this  solution  im- 
mediately into  another  vessel  where  the  silver  is  precipitated  by 
contact  with  copper.  After  the  silver  has  been  thus  completely 
removed,  the  copper  nitrate  solution  is  made  slightly  acid  and 
enters  the  electrolyzing  vat,  where  a  certain  amount  of  the  copper 

1  Borchers,  Electric  Smelting  and  Refining,  2d  English  ed.  p.  309  et  seq. 

2  Z.  f.  Elektroch.  6,  81,  (1899-1900). 


58 


APPLIED   ELECTROCHEMISTRY 


FIG.  20.  —  The  Dietzel  apparatus  for  silver 
refining 


is  deposited  as  it  passes  the  cathode.  The  arrangement  is  shown 
in  Figure  20,  which  represents  a  cross  section  of  the  dissolving 
vessel.  JOT  are  the  rotary  cylindrical  copper  cathodes,  coated 
with  a  thin  layer  of  grease  or  graphite,  on  which  the  deposition 
of  copper  takes  place.  When  the  copper  grows  out  in  the  form 

of  trees,  it  is  knocked  off. 
The  copper  cylinders  are 
suspended  on  flanged  con- 
tact rollers,  which,  when  set 
in  motion,  cause  the  cylin- 
ders to  rotate.  Thus  the 
shafts  and  driving  mecha- 
nism are  out  of  contact  with 
the  solution.  P  is  a  loose 
bottom  for  supporting  the 
material  to  be  treated,  #, 
and  is  of  hard  rubber,  cellu- 
loid, or  glass.  The  plates 
P  are  provided  with  plati- 
num wires  for  conducting  the  current  to  S.  DD  are  filter 
cloths,  the  object  of  which  is  to  catch  any  copper  falling  from 
the  cathodes  and  to  prevent  any  of  the  anodic  silver  solution 
from  rising  to  the  cathode.  The  desilverized  electrolyte  is 
admitted  from  above,  as  shown.  A  small  amount  of  silver  — 
0.03  per  cent  —  is  deposited  at  the  cathode  with  the  copper. 
The  solution  contains  from  2  to  5  per  cent  of  copper  and  0.05 
to  0.4  per  cent  of  free  nitric  acid.  The  current  density  is  1.5 
amperes  per  square  decimeter  (14  amperes  per  square  foot)  and 
the  voltage  is  from  2|  to  3  volts. 

The  electrolytic  separation  of  silver  and  gold  was  first  carried 
out  by  Wohlwill  in  1871.  These  experiments  were  made  simply 
to  reduce  silver  from  the  solution  obtained  by  boiling  the  metal 
in  sulphuric  acid.  The  electrodes  were  platinum,  and  the  silver 
was  deposited  in  loose,  pure  crystals.  When  the  silver  became 
dilute,  the  current  decomposed  the  hot  concentrated  sulphuric 
acid,  separating  sulphur.  No  copper  was  deposited  with  the 
silver,  as  copper  sulphate  is  very  slightly  soluble  in  hot  con- 


BE  FINING   OF  METALS   IN   AQUEOUS   SOLUTIONS 


59 


centrated  sulphuric  acid.  In  1873  experiments  were  made 
with  the  same  solution,  but  with  anodes  of  auriferous  silver. 
Pure  silver  crystals  were  obtained  on  the  cathode,  to  which  they 
adhered  sufficiently  well  to  be  removed  from  the  bath.  The 
anode  slime  also  adhered  firmly  to  the  anode.  The  slime  con- 
tained all  the  gold  and  most  of  the  copper.  This  process  was 
in  operation  for  some  time,  during  which  2000  kilograms  of 
silver  were  refined.  It  was  given  up,  however,  on  account  of  a 
number  of  practical  difficulties,  which  increased  when  the  pro- 
cess was  carried  out  on  a  larger  scale.  One  objection  was  the 
loss  of  silver  caused  by  the  crystals  becoming  detached  from 
the  cathode  before  it  could  be  removed  from  the  bath.  These 
fell  to  the  bottom  of  the  tank  and  became  mixed  with  the  slime 
which  also  became  detached  from  the  anode  to  a  certain  extent. 

The  process  now  most  extensively  used  for  refining  silver 
electrolytically  is  due  to  Moebius.  There  are  two  processes 
known  by  this  name,  the  old  and  the  new.  The  former  uses 
fixed  cathodes,  and  is  in  operation  at  the  Deutsche  Gold-  und 
Silber-Scheide  Anstalt  at 
Frankfurt-am-Main,  at 
the  Pennsylvania  Lead 
Company's  works  near 
Pittsburg,  and  at  Pinos 
Altos,  Mexico.3  The  new 
process  has  a  rotating 
cathode  and  is  in  opera- 
tion at  the  Guggenheim 
Works  at  Perth  Amboy, 
New  Jersey.4 

The  following  descrip- 
tion of  the  plant  of  the 
Deutsche  Gold-  und  Sil- 
ber-Scheide Anstalt  is  condensed  from  Borchers.  The  cells 
are  made  by  dividing  a  wooden  tank  12  feet  long  and  2  feet 
wide  into  7  equal  compartments.  The  anodes  and  cathodes 


FIG.  21.— Vertical  section  of  the  old  Moebius 
apparatus  for  silver  refining,  showing  anode 


»  Min.  Ind.  4,  351,  (1895). 

4  Maynard,  Eng.  and  Min.  J.  51,  556,  (1891). 


60 


APPLIED   ELECTROCHEMISTRY 


are  suspended  parallel  to  the  ends  of  the  tank,  as  shown  in 
Figures  21  and  22.  The  anodes  a  are  of  such  width  that  five 

can  be  hung  side  by  side 
across  the  width  of  the 
cell  and  are  from  6  to  10 
millimeters  thick.  The 
cathodes  k  are  thin,  rolled 
sheets  of  silver  that  ex- 
tend across  the  whole  cell. 
Each  contains  four  cath- 
odes and  three  rows  of 
anodes.  The  anodes  are 
inclosed  in  filter  cloth 
bags  for  collecting  the 
anode  mud.  Each  cath- 
ode has  two  wooden  scrap- 
ers 8  on  each  side  to  scrape 
off  the  silver,  which  falls 

FIG.  22.- Vertical  section  of  the  old  Moebius      j    to         t  covering    the 

apparatus  for  silver  refining,  showing  cathodes  J 

whole  area  of  each  cell. 

The  bottom  of  the  tray  is  of  filter  cloth  supported  by  a  wooden 
grid. 

The  electrolyte  is  an  acid  silver  nitrate  solution,  which  soon 
takes  up  copper  from  the  anodes  as  copper  nitrate.  The  con- 
centration of  the  acid  varies  from  0.1  per  cent  to  1  per  cent, 
and  the  silver  con- 
centration amounts  K 
to  about  0.5  per  cent. 
The  copper  concen- 
tration may  be  as 
high  as  4  per  cent. 

The    current   density    FIG.  23.  —  Longitudinal  section  of  the  new  Moebius 

is  largely  dependent  apparatus  for  silver  refining 

on  the  amount  of  copper  in  solution.  At  first,  when  not  much 
copper  is  present,  3  amperes  per  square  decimeter  is  allowable, 
but  when  the  concentration  increases  to  4  per  cent,  the  current 
density  must  be  reduced  to  2  amperes  per  square  decimeter  on 


REFINING   OF   METALS   IN   AQUEOUS   SOLUTIONS  61 

account  of  the  danger  of  depositing  copper  with  the  silver. 
The  principle  on  which  the  silver  is  separated  from  the  copper 
is  explained  above  under  electroanalysis.  Every  twenty-four 
hours  the  whole  apparatus  suspended  in  the  bath  is  raised  out 
and  the  silver  removed,  washed,  pressed  by  hydraulic  power, 
dried,  and  melted.  The  anode  slime  is  removed  from  the  bags 
once  or  twice  a  week.  In  the  later  form,  shown  in  Figure  23, 
the  tanks  are  14  feet  3  inches  long,  16  inches  wide,  and  7  inches 
deep.  An  endless  sheet  of  silver  (7,  -fa  inch  thick,  moves  under 
the  anodes  Gr  and  carries  the  deposited  silver  to  one  end  of  the 
tank,  where  it  is  carried  out  of  the  tank  by  the  belt  D,  and  is 
scraped  off  by  S.  Electrical  contact  is  made  by  F.  The 
anodes  are  separated  from  the  cathode  by  filter  cloth,  as  in  the 
old  process. 

G-old  Refining 

The  electrolytic  refining  of  gold  was  first  accomplished  by 
Wohlwill1  at  the  Norddeutsche  Affinerie  in  Hamburg.  The 
process  consists  in  electrolyzing  gold  anodes  in  a  hot  acid  solu- 
tion of  gold  chloride.  A  cyanide  solution  would  not  do,  be- 
cause silver  and  copper  would  be  deposited  with  the  gold. 
Wohlwill  found  that  gold  anodes  do  not  dissolve  when  electro- 
lyzed  in  a  solution  of  gold  chloride,  AuClg,  or  of  chloroauric 
acid,  HAuCl4,  but  that  in  both  cases  chlorine  is  set  free.  In 
the  solution  of  chloroauric  acid  the  chlorine  may  be  mixed 
with  oxygen  when  the  current  density  is  low  or  the  solution 
dilute.  In  order  to  have  the  gold  dissolve,  there  must  be  some 
free  chloride  present,  either  hydrochloric  acid,  which  is  com- 
monly used,  or  some  alkali  chloride.  At  a  definite  temperature 
there  is  a  definite  amount  of  free  acid  for  every  current  density 
that  will  prevent  the  evolution  of  chlorine.  The  amount  of 
free  acid  required  decreases  with  increasing  temperature. 
With  a  solution  containing  3  per  cent  of  hydrochloric  acid  and 
30  grams  of  gold  per  liter,  at  70°  C.,  as  much  as  3000  amperes 
per  square  meter  can  be  used  without  liberating  chlorine,  but 
in  practice  as  much  as  1000  amperes  per  square  meter  would 
hardly  ever  be  used,  for  other  reasons.  In  case  chlorine  ap- 
1  Z.  f.  Elektroch.  4,  379,  402,  421,  (1898). 


62  APPLIED   ELECTROCHEMISTRY 

pears  at  the  anode,  its  evolution  can  be  stopped  by  adding 
hydrochloric  acid,  or  by  raising  the  temperature. 

The  gold  is  formed  on  the  cathode  in  large  crystalline  de- 
posits which  adhere  in  such  a  way  that  they  can  be  easily 
removed  mechanically.  The  more  gold  in  solution,  the  more 
compact  the  deposit,  while  an  increase  in  the  current  density 
has  the  opposite  effect.  The  impurities  coming  from  the  anode 
also  make  the  gold  deposit  more  compact.  With  the  largest 
current  density  allowable  for  the  anode,  30  grams  of  gold  per 
liter  is  sufficiently  concentrated  for  precipitating  the  gold  in  a 
convenient  form. 

The  solution  of  the  gold  anode  shows  a  certain  similarity  to 
that  of  copper  anodes,  in  that  a  portion  of  the  gold  is  dissolved 
in  the  monivalent  state.  This  decomposes  into  trivalent  gold 
chloride  and  metallic  gold,  which  latter  goes  into  the  slimes. 
This  reaction  does  not  take  place  as  rapidly  as  with  copper, 
however,  and  the  monivalent  gold  exists  through  the  entire 
solution  and  is  even  deposited  at  the  cathode,  causing  an  in- 
crease in  the  current  yield.  The  higher  the  current  density, 
the  greater  will  be  the  potential  difference  between  the  anode 
and  the  solution,  and  the  larger  the  proportion  of  gold  that 
will  be  oxidized  to  the  trivalent  state.  This  will  make  the  loss 
in  weight  of  the  anode  more  nearly  equal  to  the  gain  at  the 
cathode.  The  following  table  illustrates  this  statement.  The 
solution  contained  50  cubic  centimeters  of  concentrated  hydro- 
chloric acid  per  liter  and  was  at  65°  or  70°  C.  2 


CURRENT  DENSITY 

ANODE  Loss  PER 

CATHODE  GAIN  PER 

AMP./SQ.  DM. 

AMP.  HR.  GRM.  GOLD 

AMP.  HR.  GRM.  GOLD 

4.4 

3.35 

3.06 

7.4 

3.02 

2.79 

15.0 

2.50 

2.48 

With  15  amperes  per  square  decimeter  more  hydrochloric  acid 
had  to  be  added  to  prevent  the  evolution  of  chlorine. 

2  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  279. 


REFINING   OF   METALS    IN   AQUEOUS    SOLUTIONS  63 

The  impurities3  in  the  anode  may  consist  of  silver,  lead, 
bismuth,  and  the  platinum  metals.  Silver  is  converted  to  silver 
chloride  which  drops  into  the  slime  or  is  removed  mechanically. 
Lead  is  changed  to  the  chloride  which  dissolves  slightly.  If 
present  to  any  considerable  extent,  it  is  precipitated  by  adding 
sulphuric  acid  to  the  solution  from  time  to  time.  The  anode 
then  becomes  covered  with  sulphate,  which  either  drops  off 
itself  or  is  removed  mechanically.  Bismuth  is  changed  to 
the  oxychloride  and  is  also  removed  from  the  anode  mechani- 
cally. Platinum  and  palladium  both  dissolve  completely,  while 
the  other  platinum  metals  go  into  the  slimes.  Platinum  can 
accumulate  in  the  solution  till  its  concentration  becomes  twice 
that  of  the  gold,  without  being  precipitated  at  the  cathode,  but 
when  the  solution  contains  5  grams  or  more  of  palladium  per 
liter,  traces  of  this  metal  are  found  in  the  gold  cathode.  The 
platinum  and  palladium  are  allowed  to  accumulate  to  this  ex- 
tent and  are  then  recovered.  Since  only  gold  is  deposited, 
while  other  metals  are  dissolved,  the  solution,  if  left  to  itself, 
would  become  poor  in  gold.  This  therefore  has  to  be  made 
up  by  adding  gold  chloride  from  time  to  time. 

Besides  the  platinum  metals,  the  slimes  contain  one  tenth  the 
weight  of  the  gold  in  the  anodes,  due  to  the  decomposition  of 
aurous  chloride,  as  explained  above.  The  gold  obtained  is  not 
infrequently  1000  fine  and  only  in  quite  exceptional  cases  is 
less  than  999.8  fine. 

At  the  mint  in  Philadelphia  *  the  cells  are  of  white  porce- 
lain 15  inches  long,  11  inches  wide,  and  8  inches  deep.  Each 
cell  contains  12  anodes  and  13  cathodes,  1J  inches  apart,  con- 
nected in  multiple.  The  anodes  are  6  inches  long,  3  inches  wide, 
and  |  inch  thick.  The  cathodes  are  fine  gold  yJ7  inch  thick. 

Electrolysis  is  also  used  for  precipitating  the  gold  from  the 
very  dilute  solution  obtained  in  the  cyanide  process.5  The  an- 
odes are  iron  plates  2  to  3  millimeters  thick,  covered  with  filter 

8  Z.  f.  Elektroch.  3,  316,  (1897).    Extract  of  the  German  patent,  No.  90,276. 

4  Electrochem.  Ind.  1, 157,  (1903).  For  the  mint  at  San  Francisco,  see  ibid. 
6,  355  and  408,  (1908). 

6  See  Cyanid  Progresse  zur  Godgewinnung,  by  Uslar  and  Erlwein,  Vol.  7,  p.  14, 
of  the  Engelhardt  Monographs;  also  Borchers,  Z.  f.  Elektroch.  7,  191,  (1901). 


64  APPLIED   ELECTROCHEMISTRY 

cloth,  and  the  cathodes  are  of  thin  lead  foil.  The  solution 
used  for  extraction  contains  from  0.01  to  0.1  per  cent  of  po- 
tassium cyanide.  The  cells  are  of  iron  and  are  7  meters  long, 
1.5  meters  wide,  and  1  meter  deep,  divided  into  several  com- 
partments. The  electrolyte  circulates  from  one  compartment 
to  another.  The  current  density  is  about  0.5  ampere  per  square 
meter  at  2  volts.5  The  gold  sticks  to  the  lead  cathodes,  which 
are  taken  out  every  month  and  melted  with  the  gold.  In  some 
places  the  iron  anodes  have  been  replaced  by  peroxidized  lead 
and  the  lead  cathodes  by  tin  plate,  on  which  the  gold  is  pre- 
cipitated as  slime.6 

Lead  Refining 

Lead  is  an  ideal  metal  to  refine  electrolytically,  on  account 
of  its  high  electrochemical  equivalent  and  of  its  relatively  high 
position  in  the  electrolytic  series.  Its  greater  tendency  to  go 
into  solution  than  that  of  most  of  the  metals  occurring  in  it  as 
impurities  makes  it  possible  to  dissolve  the  lead,  leaving  the 
impurities  behind  in  the  metallic  state.  This  avoids  contami- 
nating the  electrolyte,  which  consequently  does  not  need  fre- 
quent purification.  The  principal  electrolytic  difficulty  to 
overcome  was  to  obtain  the  lead  in  a  coherent,  compact  form, 
from  a  solution  that  would  not  be  too  expensive  to  use  on  a 
commercial  scale.  The  chloride  or  sulphate,  which  are  usually 
the  salts  employed  for  metal  refining,  cannot  be  used  in  the 
case  of  lead  on  account  of  their  insolubility.  The  problem  has 
been  solved  by  A.  G.  Betts,1  who  found  that  a  solution  of 
lead  fluosilicate  with  a  small  quantity  of  gelatine  fulfilled  the 
requirements.  The  fluosilicate  solution  is  not  the  only  one 
from  which  a  good  deposit  can  be  obtained  ;  but  it  was  selected 
on  account  of  its  low  price  as  compared  with  other  solutions 
giving  equally  good  deposits.2  The  object  in  refining  lead  is  to 
recover  the  copper,  antimony,  and  bismuth,  as  well  as  the  gold 
and  silver. 

«  Electrochem.  Ind.  2,  131,  (1904). 

1  See  Lead  Refining  by  Electrolysis,  by  A.  G.  Betts.  John  Wiley  and  Sons 
(1908).  2  Betts,  ibid.  p.  17. 


REFINING    OF   METALS    IN   AQUEOUS    SOLUTIONS  65 

The  solution  of  lead  fluosilicate  (PbSiF6)  is  prepared  by 
adding  white  lead  or  lead  carbonate  to  fluosilicic  acid.  Fluosi- 
licic  acid  is  prepared  by  allowing  a  solution  of  hydrofluoric 
acid,  made  from  sulphuric  acid  and  calcium  fluoride,  to  trickle 
through  a  layer  of  pure  sand  or  broken  quartz.  Heat  is  applied 
to  start  the  reaction,  which  then  furnishes  sufficient  heat  itself 
to  maintain  the  necessary  temperature.  No  precipitate  is 
formed  on  adding  the  lead  to  the  acid  unless  an  excess  of  lead 
is  added,3  and  the  solution  obtained  is  colorless.  The  strength 
of  the  solution  ordinarily  employed  in  practice  is  from  6  to  7 
grams  of  lead,  and  from  12  to  13  grams  of  SiF6  per  100  cubic 
centimeters.4  This  means  about  8  grams  of  free  fluosilicic  acid 
per  100  cubic  centimeters  of  solution.  The  gelatine  is  added 
to  the  solution  as  a  hot  strong  solution  of  glue.  Enough  is 
added  to  make  its  concentration  0.1  per  cent.  The  temperature 
of  the  electrolyte  has  been  found  to  have  no  effect  in  the 
character  of  the  lead  deposit.5  In  practice  about  30°  C.  is 
maintained  by  the  current  itself. 

The  impurities  in  the  anode  may  consist  of  iron,  zinc,  sulphur, 
copper,  nickel,  tin,  antimony,  arsenic,  bismuth,  cadmium,  gold, 
selenium,  and  tellurium.  Only  the  zinc,  iron,  nickel,  and  tin 
would  go  into  solution.  The  other  metals  are  all  below  lead  in 
the  electrolytic  series  and  would  therefore  remain  in  the  anode 
slime.  Zinc,  iron,  and  nickel  are  above  lead  and  would  therefore 
not  be  precipitated  from  the  solution  with  lead.  Tin,  however, 
is  so  near  lead  in  the  series  that  it  dissolves  and  precipitates 
with  the  same  facility  and  can  therefore  not  be  separated  from 
lead  electrolytically.  It  must  be  removed  by  poling,  before 
casting  the  anodes.  When  only  0.02  per  cent  of  tin  is  in  the 
anode,  it  is  found  in  the  cathode.6  With  this  exception,  the 
impurities  are  easily  prevented  from  reaching  the  cathode,  even 
when  present  in  the  anode  in  large  quantities.  Pure  lead  can 
be  obtained  when  the  anode  contains  only  65  per  cent  lead,  the 
rest  being  impurities  of  bismuth,  antimony,  arsenic,  silver,  and 

8  Betts,  I.e.  p.  30.     See  also  Senn,  Z.  f.  Elektroch.  11,  230,  (1905). 
4  Betts,  I.e.  p.  255.  5  Senn,  I.e.  •  Betts,  I.e.  p.  46. 

F 


66  APPLIED    ELECTROCHEMISTRY 

copper.7  A  low  current  density,  —  4  amperes  per  square  foot, 
—  was  required  with  anodes  of  this  composition. 

The  slime  nearly  all  adheres  to  the  anode  and  is  consequently 
easily  removed  from  the  bath.  Its  composition  of  course 
depends  on  that  of  the  anodes.  It  has  been  stated  that  the 
handling  of  the  anode  slime  has  not  been  satisfactorily  settled,8 
and  from  the  large  amount  of  space  given  to  this  subject  by 
Betts  in  his  book,  it  would  seem  to  be  an  unusually  difficult 
problem.  The  method  employed  at  Trail,  British  Columbia,  by 
the  Consolidated  Mining  and  Smelting  Company  of  Canada, 
consists  in  treating  the  slime  with  sodium  sulphide,  which 
extracts  80  per  cent  of  the  antimony  and  some  arsenic.  The 
antimony  is  then  deposited  electrolytically  on  steel  cathodes 
using  lead  anodes. 

The  cathodes  used  in  lead  refining  are  thin  sheets  of  pure  lead. 
The  current  density  allowable  depends  on  the  purity  of  the 
anodes.  As  stated  above,  anodes  containing  only  65  per  cent 
lead  can  be  refined  if  the  current  density  is  as  low  as  4  amperes 
per  square  foot.  In  practice  the  anodes  are  about  98  per  c§nt 
pure,9  and  the  current  density  is  from  12  to  16  amperes  per 
square  foot.  The  analysis  of  refined  lead  from  Trail  shows  a 
purity  of  about  99.995  per  cent.  The  average  voltage  per  tank 
is  from  0.30  to  0.38  volt  and  the  polarization  amounts  to  0.02 
volt.  The  tanks,  made  of  southern  yellow  pine,  are  arranged 
in  the  multiple  system.  The  electrolyte  is  caused  to  circulate 
by  having  the  difference  in  the  level  of  two  successive  tanks 
from  2J  to  3  inches.  Five  gallons  per  minute  is  a  fair  amount 
of  circulation  for  a  4000  ampere  tank. 

Lead  is  refined  electrolytically  at  Trail,  British  Columbia, 
New  Castle  on  Tyne,  England,  and  by  the  United  States  Metals 
Refining  Company  at  Grasselli,  Indiana.  The  capacity  of  the 
first  plant  in  1908  was  about  80  tons  a  day,  of  the  third  85  tons. 
A  detailed  description  of  the  plants  at  Trail  and  Grasseli  will 
be  found  in  Betts's  treatise,  referred  to  above. 

7  Betts,  I.e.  p.  56.  8  Min.  Ind.  15,  545,  (1906). 

•  For  the  following  statements,  see  Betts,  I.e.  p.  287,  Table  110  ;  p.  255,  Table 
91 ;  p.  287,  Table  108,  and  p.  189,  Table  73. 


REFINING   OF   METALS    IN   AQUEOUS   SOLUTIONS  67 

Zinc  Refining 

It  is  possible  to  refine  zinc  electrolytically,  but  commercial 
zinc  contains  no  metals  that  it  would  pay  to  recover,  and  the 
demand  for  very  pure  zinc  is  limited. 

The  only  impurities  occurring  in  commercial  zinc  are  iron, 
lead,  and  cadmium.  In  the  slightly  acid  chloride  solution,  con- 
taining about  56  grams  of  zinc  per  liter,  with  a  current  density 
of  1.8  to  1.9  amperes  per  square  decimeter,  zinc  can  be  freed 
from  its  impurities  to  as  great  an  extent  as  copper.  The  analysis 
of  some  refined  zinc  is  as  follows : 1 

99.955  per  cent  zinc, 
0.036  per  cent  lead, 
0.0012  per  cent  iron, 
0.0080  per  cent  cadmium. 

Though  the  refining  of  commercial  zinc  electrolytically  is 
seldom  carried  out,  certain  alloys  of  zinc  rich  in  silver,  obtained 
in  other  metallurgical  processes,  have  been  successfully  refined 
on  a  commercial  scale  at  Tarnowitz  in  Silesia.2  When  lead  con- 
taining silver  is  treated  with  zinc,  most  of  the  silver  is  taken  up 
by  the  zinc,  forming  an  alloy  which  floats  on  the  lead.  This 
zinc  scum,  containing  the  silver,  is  cast  into  anodes  one  centi- 
meter thick,  weighing  from  20  to  30  kilograms,  which  are 
electrolyzed  in  a  solution  of  zinc  sulphate.  The  composition  of 
the  anodes  is  the  following : 

Silver 11.32  per  cent 

Lead 3.13  per  cent 

Copper 6.16  per  cent 

Nickel 0.51  per  cent 

Iron 0.24  per  cent 

Zinc       78.64  per  cent 

Antimony,  arsenic,  bismuth,  traces. 

The  current  density  is  80  to  90  amperes  per  square  meter, 
requiring  1.25  to  1.45  volts.  The  purity  of  the  resulting  zinc 
is  not  given. 

1  Foerster  and  Gxinther,  Z.  f.  Elektroch.  5,  16,  (1898),  and  6,  301,  (1899). 

2  Hasse,  Z.  f.  Berg-  Hutten-  und  Salinenwesen,  45,  322,  (1897). 


CHAPTER  V 

ELECTROLYTIC   REDUCTION  AND   OXIDATION 

1.    REDUCTION 

REDUCTION  is  a  term  now  applied  to  several  really  different 
processes.  It  may  mean  the  loss  of  a  positive  electric  charge 
by  an  ion,  as  when  ferric  ion  changes  to  ferrous,  or  the  acquir- 
ing a  negative  charge,  as  when  chlorine  changes  to  a  chlorine 
ion,  or  it  may  mean  the  direct  addition  of  hydrogen  or  the 
removal  of  oxygen  from  a  molecule.  All  of  these  different 
kinds  of  reduction  may  be  produced  electrolytically  by  bring- 
ing the  substances  to  be  reduced  in  contact  with  a  cathode. 
Of  course  the  reduction  resulting  from  the  addition  of  hydro- 
gen is  dependent  on  the  deposition  of  hydrogen  on  the  cathode, 
which  reacts  while  in  the  nascent  state  with  the  reducible  sub- 
stance with  which  it  comes  in  contact.  The  loss  of  positive 
charge  may  also  be  represented  as  being  produced  by  the 
hydrogen  liberated  on  the  cathode,  while  in  the  nascent  state, 
as  illustrated  by  the  equation  : 

Fe+++  +  H  =  Fe++  +  H+. 

Reduction  by  acquiring  a  negative  charge  is  illustrated  by  the 
chlorine  electrode,  made  by  saturating  a  platinum  electrode 
with  chlorine.  When  chlorine  changes  from  the  molecular  to 
the  ionic  state  on  a  chlorine  electrode,  the  positive  current 
flows  from  the  solution  to  the  electrode  and  molecular  chlorine 
takes  a  negative  charge  : 

C12  +  2  H  =  2  Cl-  +  2  H+. 

68 


ELECTROLYTIC   REDUCTION    AND    OXIDATION  69 

Molecular  hydrogen  has  very  little  reducing  power,  and  con- 
sequently the  reducing  power  of  a  cathode  must  be  ascribed 
to  the  hydrogen  liberated  on  it  while  in  the  nascent  state. 
According  to  the  mass  action  law,  the  reducing  power  of 
nascent  hydrogen  is  proportional  to  its  concentration.  The 
potential  difference  between  the  cathode  and  the  solution  is 
also  dependent  on  the  concentration  of  the  nascent  hydrogen, 
as  can  be  shown  as  follows  :  The  potential  of  the  hydrogen 
electrode  is  given  by  the  equation1 

(1) 

where  PHa  is  the  electrolytic  solution  pressure,  and  pn+  the 
osmotic  pressure,  of  the  hydrogen  ions  in  solution.  But  P^ 
=  ktp,  in  which  &j  is  a  constant  and  p  is  the  pressure  of  the 
gaseous  hydrogen  in  contact  with  the  electrode  and  solution.2 
By  Henry's  Law,  p  must  be  proportional  to  the  concentration 
<?i,2  of  the  molecular  hydrogen  in  the  solution  immediately  on 
the  electrode.  The  concentration  of  the  molecular  hydrogen 
must  in  turn  be  proportional  to  the  square  of  the  concentration 
of  the  nascent  hydrogen  on  the  electrode,  since  the  reaction  is 
2  H  =  H2,  and  by  the  mass  action  law,  for  equilibrium, 


The  electrolytic  solution  pressure  is  therefore  proportional  to 
the  concentration  of  the  nascent  hydrogen  on  the  cathode, 
since,  as  explained  above, 


Obviously,  any  pf  the  quantities  proportional  to  P2Ha  may  be 
substituted  in  equation  (1).     Substituting  &3<?H, 

(2) 

which  shows  that  the  potential  of  the  cathode  is  a  measure  of  its 
reducing  power,  since  it  is  determined  by  the  concentration  of 

1  Le  Blanc,  Electrochemistry,  p.  183,  (1907). 
2Le  Blanc,  Electrochemistry,  p.  195,  (1907). 


70 


APPLIED   ELECTROCHEMISTRY 


the  nascent  hydrogen,  eH,  assuming  eH+,  the  concentration  of 
hydrogen  ions,  is  constant. 

If  the  cathode  potential  is  to  be  expressed  in  terms  of  the 
pressure  of  the  hydrogen  gas  in  contact  with  it  and  the  solu- 
tion, it  may  be  done  by  transforming  equation  (1)  and  substi- 
tuting as  follows : 


ETlog 


(3) 


These  equations  give  only  the  numerical  value  of  the  poten- 
tial difference  between  the  electrode  and  the  solution,  and  take 
no  account  of  which  is  positively  and  which  is  negatively 
charged.  The  charge  on  any  electrode  whose  potential  can  be 
represented  by  a  formula  similar  to  those  above  may  be  either 
positive  or  negative,  depending  on  whether  the  value  of  the 
fraction  following  the  logarithm  sign  is  greater  or  less  than  one. 

The  two  principal  advantages  of  electrolytic  reduction,  over 
that  produced  by  adding  some  chemical  reducing  agent,  which 
must  of  course  be  oxidized  itself,  is  that  no  such  oxidized  sub- 
stance is  left  in  the  solution,  and  that  the  reducing  power  of  a 
cathode  can  be  varied  within  wide  limits  and  in  small  steps. 
One  method  of  varying  the  reducing  power  of  the  cathode  is  to 
vary  the  current  density  on  it.  The  increase  in  the  potential 
difference  that  can  be  obtained  in  this  way,  however,  is  not 
very  great.  This  is  shown  in  Table  7,  in  which  are  given  the 
current  densities  and  the  corresponding  potentials  referred  to 
the  normal  hydrogen  electrode  as  zero,  of  cathodes  of  different 
metals  dipping  in  twice  normal  sulphuric  acid : 3  It  will  be 

TABLE  7 


AMPERES  PEE 
SQUARE  CM. 

MEKCUEY 

TIN 

GOLD 

COPPEB 

NICKEL 

PLATINIZED 
PLATINUM 

0.01 

1.19 

0.97 

0.74 

0.57 

0.56 

0.05 

0.05 

1.26 

1.11 

0.89 

0.70 

0.67 

0.06 

0.11 

1.30 

1.16 

0.95 

0.77 

0.73 

0.08 

0.15 

1.32 

1.18 

1.09 

0.82 

0.76 

0.09 

8  Tafel,  Z.  f.  phys.  Ch.  50,  710,  (1906). 


ELECTROLYTIC    REDUCTION   AND   OXIDATION  71 

seen  that  the  potential  difference  between  electrode  and  solu- 
tion does  not  increase  much  with  increasing  current  density, 
but  that  for  a  given  current  density  it  is  quite  different  for 
different  metals.  This  is  due  to  what  has  been  called  the  over- 
voltage  for  the  metal  in  question,  which  means  the  excess 
voltage  necessary  to  liberate  a  gas  on  the  metal  over  that 
necessary  to  liberate  it  on  a  reversible  electrode.4  The  reduc- 
ing power  of  a  cathode  can  therefore  be  greatly  varied  by  mak- 
ing the  cathode  of  different  metals. 

This  change  in  reducing  power  may  be  made  to  appear  in 
much  larger  numerical  values  by  calculating  the  number  of  at- 
mospheres to  which  these  higher  potentials,  due  to  overvolt- 
age,  correspond  ;  that  is,  by  assuming  that  the  higher  potentials 
are  produced  by  compressing  the  gaseous  hydrogen  surround- 
ing a  reversible  electrode,  and  computing  the  number  of  atmos- 
pheres pressure  that  would  be  necessary  to  make  the  potential 
difference  between  electrode  and  solution  some  definite  amount, 
0.1  volt,  for  example.  This  can  be  done  by  writing  the  expres- 
sion for  the  electromotive  force  of  the  cell : 


at  1  atmosphere 


Electrolyte 


Pt  +  H2  at 

x  atmospheres, 


and  placing  it  equal  to  0.1  volt.     The  electromotive  force  of 
this  cell  by  (3)  is  then : 

RT,      x     0.058 , 


Q%. 

Solving  this  equation  for  x  gives  2800  atmospheres.  For  0.2 
volt  the  value  of  x  is  8  million  atmospheres.  This  is  the  mean- 
ing of  the  statement  frequently  met  with,6  that  the  pressure 
of  the  hydrogen  evolved  by  electrolysis  can  be  increased  to 
millions  of  atmospheres.  The  values  thus  calculated,  however, 
can  hardly  represent  the  physical  state  of  the  gas  evolved  on 
a  cathode. 

Another   important   factor  in  electrolytic  reduction  is  the 

*  Le  Blanc,  Electrochemistry,  p.  287,  (1907). 

*  Nernst,  Theoretische  Chemie,  6th  ed.  p.  756,  (1909). 


72  APPLIED   ELECTROCHEMISTRY 

catalytic  effect  of  the  metal  composing  the  cathode.  As  a 
result  of  this  effect  a  substance  may  be  more  easily  reduced  on 
one  cathode  than  another,  even  though  the  overpressure  is  the 
same  for  both  cathodes.6 

The  electrolytic  reduction  of  galena,  or  lead  sulphide,  in  a 
sulphuric  acid  solution  was  carried  out  for  a  while  on  a  large 
scale  at  Niagara  Falls,  but  had  to  be  given  up  eventually 
on  account  of  the  poisonous  effect  of  the  hydrogen  sulphide 
produced. 

The  galena,  which  had  been  ground  to  pass  a  40  to  50  mesh 
sieve,  was  spread  in  a  layer  J  inch  thick  and  covered  with 
dilute  sulphuric  acid.7  The  current  density  was  30  amperes 
per  square  foot,  and  the  current  efficiency  was  about  66  per 
cent.8  About  97  per  cent  of  the  lead  sulphide  was  reduced  to 
spongy  lead,  which  was  washed  free  of  sulphuric  acid,  and  con- 
verted into  litharge  by  roasting. 

In  case  the  substance  to  be  reduced  is  in  solution,  it  must  be 
prevented  from  coming  in  contact  with  the  anode,  where  it 
would  be  oxidized  again.  This  is  accomplished  by  separating 
the  anode  from  the  cathode  compartment  by  some  kind  of 
diaphragm,  such  as  porous  clay,  that  allows  the  electrolytic 
passage  of  the  current,  but  which  prevents  the  mechanical 
mixture  of  the  liquids  in  the  two  compartments.  An  example 
of  this  kind  is  the  production  of  chromous  sulphate  from  chromic 
sulphate.  The  solution  contains  500  grams  of  chromic  sulphate 
in  500  cubic  centimeters  of  concentrated  sulphuric  acid,  and  is 
electrolyzed  on  a  lead  cathode  with  0.1  to  0.15  ampere  per 
square  centimeter.  The  blue-green  chromous  sulphate  deposits 
on  the  cathode,  as  the  solution  about  the  cathode  becomes  satu- 
rated with  it.9 

6  Foerster,  Elektrochemie  wasseriger  Losungen;  p.  315,  (1906). 

7  Salom,  Trans.  Am.  Electrochem.  Soc.  1,  87,  (1902). 

8  Salora,  Trans.  Am.  Electrochem.  Soc.  4,  101,  (1903). 

9  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  319,  (1905). 


ELECTROLYTIC  REDUCTION  AND  OXIDATION  73 

2.    OXIDATION 

The  oxidizing  power  of  an  anode  is  related  to  the  potential 
difference  between  the  electrode  and  the  solution  in  the  same 
way  as  the  reducing  power  of  a  cathode  and  the  potential  dif- 
ference between  it  and  the  solution.  There  is  also  an  over- 
pressure for  oxygen  on  different  metals,  as  in  the  case  of 
hydrogen.1  The  results  of  the  following  table  were  obtained 
in  a  normal  solution  of  potassium  hydrate.  The  potential  dif- 
ferences given  between  anode  and  solution  were  measured  when 
oxygen  first  appeared  on  the  anode  against  a  hydrogen  elec- 
trode in  the  same  solution. 

TABLE  8 
Potential  Difference  between  Anode  and  Solution  when  Oxygen  first  Appears 


METAL 

POTENTIAL 

Gold      

175 

1  67 

1  65 

1  65 

Silver    

1  63 

Lead      ••••••••• 

1  53 

1.48 

1  47 

147 

Cobalt  

136 

Nickel,  smooth   

135 

Nickel  spongy    

128 

The  number  of  metals  that  can  be  used  as  anode  is  much  less 
than  those  that  can  be  used  as  cathode,  and  is  limited  to  those 
metals  that  would  not  be  dissolved  by  an  action  of  the  current. 
Platinum,  lead,  and  carbon  are  the  principal  materials  for  un- 
attackable  anodes  in  acid  solutions,  while  besides  these  both 
nickel  and  iron  may  be  used  in  alkaline  solutions. 

Coehn  and  Osaka  also  found  a  decomposition  point  of  1.1 
volts  for  all  of  the  metals  investigated,  which  they  identified 

1  Coehn  and  Osaka,  Z.  f.  anorg.  Ch.  34,  86,  (1903). 


74  APPLIED   ELECTROCHEMISTRY 

with  the  value  of  the  hydrogen-oxygen  cell,  then  thought  to  be 
1.06  volts.  The  true  value  of  this  cell,  however,  has  since  been 
found  to  be  1.22  volts,2  so  that  their  first  point  cannot  have  this 
significance.  The  overvoltage  of  a  spongy  nickel  electrode  is 
evidently  very  small,  for  its  value  in  the  above  table  is  only 
a  little  greater  than  1.22  volts,  the  true  potential  of  an  oxygen 
electrode,  assuming  a  hydrogen  electrode  in  the  same  solution 
equal  to  zero. 

There  is  also  a  catalytic  effect  of  the  anode  material  on  oxi- 
dation, which  may  be  of  more  practical  importance  than  the 
overpressure.  For  example,  the  yield  in  oxidizing  iodic  to 
periodic  acid  on  smooth  platinum  was  found  to  be  1  per  cent, 
on  platinized  platinum  3  per  cent,  and  on  lead  peroxide  100  per 
cent,  though  the  potential  differences  between  the  anodes  and 
the  solution  were  1.72,  1.48,  and  1.52  volts  respectively.3  In 
the  oxidation  of  chromium  sulphate,  described  below,  smooth 
platinum  anodes  give  practically  no  yield  of  chromate,  while 
with  lead  peroxide  anodes  current  yields  between  20  and  97 
per  cent  are  obtained,  depending  on  the  concentration  of  the 
chromium  sulphate,  though  the  overpressure  of  oxygen  on  the 
peroxide  is  only  a  few  hundredths  of  a  volt  higher  than  on 
platinum.4 

The  following  are  some  of  the  most  important  technical  ap- 
plications of  electrolytic  oxidation. 

In  dye  works,  solutions  of  sodium  or  potassium  bichromate 
and  sulphuric  acid  are  used  for  oxidizing  anthracene  to  anthra- 
chinon  : 

,CH,  '    CO 


, 

H4/  I 
CH 


CO 


The  bichromate  is  thereby  reduced  to  chromium  sulphate  and 
must  be  regenerated  before  it  can  be  used  again.  Formerly 
this  was  accomplished  by  precipitating  with  calcium  hydrate 

2  Nernst,  Z.  f.  Elektroch.  11,  835,  (1905)  ;  Haber,  ibid.  834  ;  Lewis,  Journ. 
Am.  Chem.  Soc.  28,  185,  (1906). 

»  Mtiller,  Z.  f  .  Elektroch.  10,  61,  and  62,  (1904). 
*  Mtiller  and  Seller,  Z.  f.  Elektroch.  11,  863,  (1905). 


ELECTROLYTIC   REDUCTION   AND   OXIDATION  75 

and  heating  the  resulting  pasty  material,  consisting  of  chromium 
oxide,  calcium  hydrate,  and  calcium  sulphate,  to  red  heat. 
This  treatment  produces  calcium  chromate,  which,  when  treated 
with  sodium  sulphate,  gives  sodium  chromate  and  calcium  sul- 
phate. On  removing  the  insoluble  calcium  sulphate  the  sodium 
chromate  can  be  used  for  oxidation.  This  method  is  uneco- 
nomical on  account  of  the  loss  of  sulphuric  acid  and  of  chromium 
which  it  involves,  and  it  has  been  superseded  by  the  electro- 
lytic process  patented  in  1898  by  the  Farbewerke  vorm.  Meister, 
Lucius,  und  Brunig.5  This  process  consists  in  oxidizing  on  a 
lead  peroxide  anode  a  solution  of  chromium  sulphate  contain- 
ing free  sulphuric  acid,  in  the  anode  compartment  of  a  lead- 
lined  electrolytic  cell.  The  anode  and  cathode  compartments 
are  separated  by  a  diaphragm.  The  chromium  is  oxidized  from 
a  cation  to  an  anion  in  changing  from  a  chromium  salt  to 
a  chromate,  and  at  the  same  time  sulphuric  acid  concentrates 
in  the  anode  compartment,  due  to  the  migration  of  the  sulphate 
ions.  After  using  the  anode  liquid  for  oxidation,  it  is  first 
placed  in  the  cathode  compartment,  where  the  sulphuric  acid 
concentration  decreases,  after  which  it  is  again  oxidized. 

It  is  very  difficult  to  construct  diaphragms  of  size  great 
enough  for  technical  use  that  can  resist  the  action  of  the 
chromic  acid  produced.  Le  Blanc,6  after  a  number  of  experi- 
ments, produced  diaphragms  consisting  of  25  per  cent  alumina 
and  75  per  cent  silica,  which  he  considered  satisfactory  at  the 
time,  but  it  seems  eventually  not  to  have  been  successful,  for  he 
has  since  patented  a  process  for  this  oxidation  in  which  the  two 
compartments  are  separated  by  a  partition  reaching  not  quite 
to  the  bottom  of  the  cell,  in  place  of  a  conducting  diaphragm.7 
The  liquid  is  circulated  from  the  cathode  to  the  anode  com- 
partment. 

Another  example  of  technical  oxidation  is  the  production  of 
insoluble  salts  and  oxides  of  metal  by  a  process  patented  in 
1894  by  C.  Luckow.8  The  difficulty  encountered  in  the  electro- 

6  Z.  f.  Elektroch.  6,  266,  (1899).  6  Z.  f.  Elektroch.  7,  290,  (1905). 

7  Z.  f.  Elektroch.  13,  791,  (1907)  ;  14,  12,  (1908). 

8  Borchers,  Z.  f.  Elektroch.  3,482,  (1897). 


76  APPLIED   ELECTROCHEMISTRY 

lytic  manufacture  of  insoluble  salts  or  other  compounds  by  the 
oxidation  of  the  metallic  anode  is  that  the  compound  sticks  to 
the  anode  and  produces  a  high  electrical  resistance.  In  the 
Luckow  process  this  difficulty  is  overcome  by  using  a  1^  per 
cent  solution  of  a  mixture  of  two  salts,  the  anion  of  one  forming 
a  soluble  salt  with  the  metal  of  the  anode,  and  the  anion  of  the 
other  forming  the  insoluble  salt  desired.  The  mixture  consists 
of  80  parts  of  the  first,  or  auxiliary  salt,  to  20  parts  of  the 
second,  or  principal  salt.  The  anions  of  the  principal  salt, 
being  present  in  a  much  smaller  number  than  those  of  the  aux- 
iliary salt,  are  soon  used  up  in  the  layer  of  solution  next  to  the 
anode,  and  are  replaced  slowly  because  the  auxiliary  anions 
carry  most  of  the  current  on  account  of  their  greater  number. 
The  ions  of  the  anode,  on  dissolving,  do  not,  therefore,  come  in 
contact  with  the  anions  of  the  principal  salt  directly  on  the 
anode,  but  the  precipitate  is  formed  a  slight  distance  from  the 
anode  and  therefore  does  not  stick,  but  falls  down  to  the  bottom 
of  the  cell.9 

If  the  auxiliary  salt  is  not  added,  the  salt  desired  cannot  be 
produced  with  a  satisfactory  yield,  for  either  the  anode  is 
covered  with  an  insulating  layer  of  the  insoluble  salt,  or  the 
desired  salt  is  not  produced  at  all.  For  example,  in  electro- 
lyzing  a  lead  anode  in  a  0.12  per  cent  solution  of  potassium 
chromate,  a  mixture  of  lead  peroxide  and  lead  chromate  formed 
on  the  anode,  but  practically  no  yield  of  lead  chromate  could  be 
obtained.10  Even  when  the  two  salts  are  in  the  right  propor- 
tion, if  the  solution  is  too  concentrated,  the  same  difficulties  are 
encountered. 

In  manufacturing  white  lead,  for  which  the  Luckow  process 
seems  well  suited,  a  1J  per  cent  solution  of  a  mixture  of  80  per 
cent  sodium  chlorate  and  20  per  cent  sodium  carbonate  is  elec- 
trolyzed  with  a  soft  lead  anode  and  a  hard  lead  cathode,  with  a 
current  density  of  0.5  ampere  per  square  decimeter.  Carbon 
dioxide  is  passed  through  the  solution  over  the  anode  to  replace 
that  removed  by  the  lead.  If  enough  of  the  gas  is  passed 

•  Le  Blanc  and  Bindschedler,  Z.  f.  Elektroch.  8,  262,  (1902). 
loisenburg,  Z.  f.  Elektroch.  9,  275,  (1903). 


ELECTROLYTIC    REDUCTION   AND    OXIDATION 


77 


through  the  solution,  the  pure  carbonate  of  lead  is  produced,  and 
in  order  to  get  basic  carbonate  the  quantity  of  carbonic  acid 
must  be  limited.  The  same  result  can  be  accomplished  by 
diluting  the  carbonic  acid  with  an  indifferent  gas,  such  as  air, 
and  passing  an  excess  through  the  solution.  Table  9  shows  the 
relation  between  the  concentration  of  the  gas  and  the  product  : 10 

TABLE  9 


EATIO  OF  AIR  TO  C02  BY 
VOLUME 

PER  CENT  PbO  IN  PRODUCT 

PER  CENT  PbO  IN  WHITE  LEAD 
2PbC03.Pb(OH)2 

97:3 

86.50 

86.31 

80:20 

85.92 

86.31 

60:40 

83.41 

86.31 

It  is  evident  that  the  carbon  dioxide  is  too  concentrated  when 
mixed  with  air  in  the  proportion  of  40  to  60. 

In  producing  oxides  by  this  metal,  the  mixture  of  salt  elec- 
trolyzed  contains  only  0.5  per  cent  of  the  auxiliary  salt.  For 
lead  peroxide,  a  1J  per  cent  solution  of  a  salt  mixture  con- 
sisting of  99.5  per  cent  of  sodium  sulphate  and  0.5  per  cent  of 
sodium  chlorate,  acidified  with  sulphuric  acid,  is  used.  The 
current  density  on  the  anode  is  about  0.2  ampere  per  square 
decimeter. 

The  electrolytic  method  of  producing  iodoform  has  almost 
entirely  displaced  the  older  chemical  method.  The  electrolytic 
method  was  patented  as  early  as  1884  by  the  Chemische  Fabrik 
auf  Aktien,  vorm.  E.  Schering.11  According  to  this  patent, 
iodoform  is  made  by  electrolyzing  a  hot  solution  of  potassium 
iodide  and  alcohol,  through  which  carbon  dioxide  is  passed. 
The  addition  of  alkali  carbonate  also  was  found  advantageous, 
when  the  study  of  this  subject  was  taken  up.11  The  final 
result  of  the  chemical  reaction  of  iodine  on  alcohol  in  the  pres- 
ence of  alkali  carbonate  is  represented  by  the  equation  : 

C2H5OH  +  10  I  +  H20  =  CHI3  +  C02  +  7  HI. 

11  Elbs  and  Herz,  Z.  f.  Elektroch.  4,  113,  (1897). 


78  APPLIED   ELECTROCHEMISTRY 

The  iodine  may  be  furnished  by  liberating  it  electrolytically 
from  potassium  iodide  on  a  platinum  anode.  This  is  an  oxida- 
tion, since  the  iodine  ion  is  deprived  of  a  negative  charge. 
A  suitable  solution  for  this  electrolysis  is  made  up  of  5  grams 
of  sodium  carbonate,  10  grams  of  potassium  iodide,  20  cubic 
centimeters  of  alcohol,  and  100  cubic  centimeters  of  water. 

The  iodine  does  not  act  on  the  alcohol  directly,  as  given  by 
the  above  equation,  but  first  forms  alkali  hypoiodite  with  the 
hydroxyl  ions  from  the  hydrolysis  of  the  carbonate  according 
to  the  equation  : 


The  hypoiodite  is  hydrolytically  dissociated  as  follows  : 
NalO  +  H20  =  NaOH  +  HIO. 

Hypoiodous  acid,  being  unstable,  decomposes  in  the  following 
two  ways  :  12 

3HIO  =  HIO3  +  2HI 

and          C2H5OH  +  5  HIO  =  2  HI  +  CHI3  +  CO2  +  4  H2O. 

That  iodine  does  not  act  directly  on  alcohol  was  proved  by 
determining  the  decomposition  point  of  the  solution  with  and 
without  the  addition  of  alcohol.  If  the  alcohol  combined  di- 
rectly with  the  iodine  liberated,  it  would  reduce  the  concen- 
tration of  the  free  iodine  on  the  electrode  and  lower  the  de- 
composition point.  Since  the  potential  of  an  iodine  electrode 
is13 


in  which  <7Ia  is  the  concentration  of  the  free  iodine  and  <7j_  is 
that  of  the  iodine  ions,  any  substance  in  solution  which  reduces 
the  value  of  (7Is  will  change  the  numerical  value  of  the  potential. 
It  was  found  that  alcohol  has  not  such  depolarizing  effect, 
but  that  the  carbonate  has,  which  fact  points  to  the  explana- 
tion given  above. 

12  Dony-H^nault,  Z.  f.  Elektroch.  7,  67,  (1900). 

»  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  124,  (1906). 


ELECTROLYTIC   REDUCTION   AND    OXIDATION  79 

A  high  current  density  decreases  the  yield,  since  a  greater 
concentration  of  alkali  hypoiodite  tends  to  produce  a  larger 
amount  of  iodate.  With  a  solution  made  up  of  10  grams  of 
alcohol,  5  grams  of  sodium  carbonate,  16  grams  of  potassium 
iodide,  and  100  grams  of  water,  Foerster  and  Meves  obtained 
the  following  results  : 14 


AMPERES  PER  SQUARE  DECIMETER 

CURRENT  YIELD  IN  PER  CENT  OP  THE 
THEORETICAL 

1 

95-97 

2 

80-93 

3 

73-79 

Since  iodine  is  continuously  removed  from  the  solution,  and  car- 
bon dioxide  is  added,  the  alkali  carbonate  will  increase  in  con- 
centration. When  it  had  increased  to  six  times  the  amount 
given  in  the  formula  just  above,  the  yield  fell  to  43  per  cent, 
with  a  current  density  of  2  amperes  per  square  decimeter,  and 
the  iodoform  formed  in  a  thick  crust  on  the  anode  and  con- 
tained free  iodine.  The  carbonate  should  therefore  not  be 
allowed  to  accumulate  to  this  extent. 

Bromoform  and  chloroform  cannot  be  produced  in  this  way, 
but  other  oxidation  products  are  formed,  especially  chlor-  or 
brom-  aldehyde.  This  is  due  to  the  higher  potential  at  which 
bromine  and  chlorine  are  liberated,  which  is  sufficient  to  oxi- 
dize the  alcohol.  Bromoform  can  be  produced  with  a  good 
yield,  however,  if  acetone  is  used  in  place  of  alcohol. 

i*  Z.  f.  Elektroch.  4,  268,  (1897). 


CHAPTEE  VI 
THE  ELECTROLYSIS  OF  ALKALI  CHLORIDES 

1.    THEORETICAL  DISCUSSION 
The  Chemical  Action  of  Chlorine  on  Water  and  Alkali  Hydrate 

THE  electrolysis  of  sodium  and  potassium  chlorides  is  one  of 
the  largest  electrochemical  industries  that  is  carried  out  in 
aqueous  solution.  Chlorine  and  sodium  hydrate,  hypochlorite,. 
chlorate,  or  perchlorate  may  be  produced  from  sodium  chloride, 
depending  on  the  conditions  of  the  electrolysis. 

The  first  products  obtained  on  electrolyzing  the  solution 
of  an  alkali  chloride  are  chlorine  at  the  anode  and  alkali 
hydrate  at  the  cathode.  If  these  two  primary  products  are 
the  ones  desired,  they  must  not  be  allowed  to  mix,  while  if 
hyperchlorite,  chlorate,  or  perchlorate  is  desired,  the  chlorine 
and  hydrate  must  be  allowed  to  react  with  each  other.  Before 
describing  the  electrolysis  of  the  alkali  chlorides,  it  will  be  nec- 
essary to  give  a  brief  account  of  the  purely  chemical  reactions. 
that  take  place  between  chlorine  and  the  alkali  hydrates,  and 
between  chlorine  and  pure  water. 

Chlorine  enters  into  a  reaction  with  pure  water  to  a  slight 
extent,  according  to  the  equilibrium  represented  by  the  equa- 
tion :  1 

C12  +  H2O  ^±  H+  +  Cl-  +  HOC1.  (1) 

The  equilibrium  constant  of  this  reaction  is 


=2570, 


i  Jakowkin,  Z.  f.  phys.  Ch.  29,  613,  (1899). 
80 


ELECTEOLYSIS    OF   ALKALI   CHLORIDES  81 

if  the  concentrations  are  taken  in  moles  per  liter.2  It  is  evi- 
dent from  the  large  value  of  this  constant,  and  from  the  fact 
that  the  concentration  of  free  chlorine  in  a  saturated  solution 
at  25°  is  only  0.064  mole  per  liter,3  that  the  concentration  of 
hydrochloric  and  hypochlorous  acids  that  can  exist  together  in 
solution  are  very  small.  If  brought  together  in  greater  con- 
centrations, chlorine  will  be  produced,  according  to  equation 
(1),  taken  from  right  to  left. 

If  chlorine  is  passed  into  a  solution  of  alkali  hydrate,  the 
following  reaction  between  the  chlorine  and  hydroxyl  ions 
takes  place  :  C12  +  OH-  ^  HOC1  +  Cl~  (2) 

The  value  of  the  equilibrium  constant  of  this  equilibrium  is 
given  by  the  following  equation  :  4 


which  is  derived  from  the  equations 

Cci.  Kw       1.4  x  10-14 

-  --       l2     --  =2570  and  CH+  =  ^  =  —  ^-     -• 

^H+  *  ^Cl-   *  ^HOCl  ^OH-  ^'OH- 

In  all  of  these  equations  the  concentrations  are  in  moles  per 
liter.  Hypochlorous  acid  then  reacts  with  the  unchanged 
hydrate  to  produce  a  hypochlorite,  and  this  reaction  also 
leads  to  an  equilibrium  represented  by  the  equation  : 

HOC1  +  OH-  ^>  OC1-  +  H2O,  (4) 

for  which  the  equilibrium  constant  is 

•  COH_ 


This  is  the  hydrolysis  constant  of  the  hypochlorite.     The  value 
of  K3  can  be  obtained  from  the  dissociation  constant  of  hypo- 

chlorous  acid  :  6  r  r 

K  =  ^oci-  •  ^H+  =  3.  7  x  lQ-8, 


2  Luther,  Z.  f.  Elektroch.  8,  602,  (1902). 

3  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  341,  (1905). 

4  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  921,  (1902).     The  value  of  Kw  is 
taken  from  van  Laar,  Theoretische  Elektrochemie,  p.  174,  (1907). 

6  Sand,  Z.  f.  phys.  Ch.  48,  610,  (1904). 


82  APPLIED   ELECTROCHEMISTRY 

and  the  dissociation  constant  of  water: 

KW  =  CH+  •  COH- =  1.4  X  10-". 
Dividing  Kw  by  K4, 

KW  _  CH+  •  COH-  •  CHOCI  _  £   _  1.4  X  10~14  _.  3  g  x 
K4  COC1-.CH+  "8.7x10-8 

When  therefore  any  quantity  of  chlorine  acts  on  alkali  hydrate, 
the  resulting  quantities  of  hydrate,  chlorine,  chloride,  hypo- 
chlorous  acid,  and  hypochlorite  are  determined  by  the  equilibria 
represented  by  equations  (2)  and  (4).  Only  when  there  are 
at  least  two  equivalents  of  hydrate  to  one  mole  of  chlorine  does 
the  following  reaction  hold  : 

C12  +  2  NaOH  =  NaCl  +  NaOCl  +  H2O.  (5) 

This  is  the  sum  of  equations  (2)  and  (4),  and  is  the  one  usually 
given  to  represent  the  reaction  between  chlorine  and  hydrate. 
Since  the  equilibria  represented  by  equation  (3)  and  the  equa- 
tion for  the  value  of  K3  exist  simultaneously,  the  values  of  COII_ 
and  CHOCI  are  the  same  in  both.  From  the  equation  for  K3, 

CHOCI  _  vr      COC1_ 
P  3  *  772       » 

^OH-  *-*  OH- 

and  combining  this  with  the  equation  for  K2, 


^Cl-  ^OH-  ^  OH- 

This  equation  is  convenient  for  predicting  what  effect  a  change 
in  the  concentration  of  one  substance  will  have  on  that  of  the 
others. 

From  equation  (6)  it  would  seem  that  for  a  given  value  of 
Ccla  and  CC1_,  the  value  of  COC1_  could  be  increased  in  propor- 
tion to  the  value  of  COH_.  This  would  be  true,  if  the  concen- 
tration of  the  hypochlorite,  COC1_,  were  not  limited  by  another 
reaction,  —  the  oxidation  of  hypochlorite  to  chlorate  by  hypo- 
chlorous  acid,  according  to  the  equation : 6 

2  HOC1  +  QC1-  =  ClOg  +  2  Cl-  +  2  H+.  (7) 

•  Foerster  and  Jorre,  J.  f .  prakt.  Ch.  59,  53,  (1899)  ;  Foerster,  ibid.  63,  141, 
(1901). 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  83 

The  free  hydrochloric  acid  then  sets  free  an  equivalent  amount 
of  hypochlorous  acid  according  to  the  equation  : 

2  H+  +  2  Cl-  +  2  OC1-  =  2  HOC1  +  2  Cl~,  (8) 

and  the  hypochlorous  acid  thus  set  free  oxidizes  more  hypo- 
chlorite.  This  process  continues  until  all  of  the  hypochlorite 
has  been  changed  to  chlorate. 

Substituting  the  numerical  values  of  K2  and  K3  in  (6),  we 
have 

1.4  xlO-tto^-  (9) 


In  order  to  illustrate  the  use  of  the  above  equation,  the  rela- 
tive concentrations  of  chlorine  ions,  hydroxyl  ions,  free  chlorine, 
and  hypochlorous  acid  in  a  neutral  solution  normal  with  respect 
to  hypochlorite  ions  will  be  calculated.  From  the  value  of  K3, 
the  values  of  CHOC1  and  COH_  are  each  6.2  •  10~4  mole  per  liter, 

and  from  (9)  the  value  of  the  fraction  ^-  is  3.6  x  lO'11.     If 

^ci- 

the  concentration  of  chlorine  ions  is  also  normal,  that  of  the 
free  chlorine  is  only  3.6  x  10~n  mole  per  liter.4 

If  chlorine  is  led  into  a  solution  of  alkali  hydrate,  nothing 
but  hypochlorite  and  chloride  are  produced  as  long  as  some  of 
the  hydrate  remains  unneutralized.  This  is  because  the  excess 
of  hydroxyl  ions  drives  back  the  hydrolysis  of  the  hypochlorite 
and  therefore  prevents  the  formation  of  a  free  hypochlorous 
acid.  When  an  amount  of  chlorine  equivalent  to  the  hydrate 
has  been  added,  there  is  still  so  small  a  quantity  of  free  hypo- 
chlorous  acid  present  that  the  solution  is  fairly  stable.  An 
excess  of  chlorine,  however,  increases  the  concentration  of  the 
free  hypochlorous  acid  to  such  an  extent  that  the  hypochlorite 
is  rapidly  oxidized  to  chlorate,  according  to  equation  (7).  The 
fact  that  an  excess  of  chlorine  was  necessary  to  produce  chlo- 
rate was  first  discovered  by  Gay-Lussac.7  The  addition  of  a 
small  quantity  of  free  acid  would  have  the  same  effect  as  an 
excess  of  chlorine,  for  it  would  set  free  hypochlorous  acid. 

7  Liebig  Ann.  43,  153,  (1842). 


84  APPLIED    ELECTROCHEMISTRY 

If  chlorate  were  formed  only  by  means  of  free  hypochlorous 
acid,  hypochlorite  would  be  more  stable  the  greater  the  excess 
of  hydroxyl  ions  in  the  solution.  Chlorate  is  produced,  how- 
ever, slowly  in  alkaline  solutions,  presumably  by  the  reaction 

3  NaOCl  =  NaClO3  +  2  NaCl.  (10) 

Hypochlorous  acid  breaks  up  in  exactly  the  same  way,  when  it 
decomposes  of  itself.  The  solution  has  to  be  heated  to  70°  C.  to 
make  this  reaction  proceed  with  an  appreciable  velocity,6  and 
it  is  also  catalyzed  by  light.  With  increasing  alkalinity  the 
velocity  of  the  reaction  increases  somewhat,  and  it  is  always 
accompanied  by  the  reaction : 

2  NaOCl  =  O2  +  2  NaCl.  (11) 

The  last  reaction  is  catalyzed  by  some  metallic  oxides,  espe- 
cially by  the  oxide  of  cobalt,  to  such  an  extent  that  all  of  the 
hypochlorite  can  be  decomposed  in  this  way  without  forming 
any  chlorate.6 

Perchlorate  cannot  be  formed  by  the  further  action  of 
chlorine  on  chlorate,  but  is  produced  by  the  decomposition  of 
chlorate,  as  will  be  explained  below. 

The  Electrolysis  of  Alkali  Chloride  on  Smooth  Platinum  Elec- 
trodes without  a  Diaphragm 

If  a  concentrated  neutral  solution  of  alkali  chloride  is  electro- 
lyzed  between  smooth  platinum  electrodes,  the  alkali  is  de- 
posited on  the  cathode  and  reacts  with  the  water  according  to 
the  equation : 

2  Na  +  2  H2O  =  2  NaOH  +  H2.  (12) 

The  hydrogen  produced  escapes,  unless  it  is  used  up  in  reduc- 
ing some  substance  in  the  solution.  On  the  anode,  chlorine  is 
liberated  from  the  ionic  form  to  free  chlorine,  as  follows : 

2C1-  +  2F=C12.  (13) 

The  liberated  chlorine  partly  dissolves  in  the  water  and  at 
first  partially  escapes  from  the  solution.  Soon,  however,  the 
alkali  hydrate  produced  at  the  cathode  and  the  dissolved 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  85 

chlorine  are  brought  together  by  the  stirring  produced  by  the 
escaping  hydrogen,  and  after  this  no  more  chlorine  escapes 
from  the  solution.  Chlorine  and  alkali  hydrate  are  produced 
in  equivalent  quantities,  so  that  the  equation  (5), 

C12  +  2  NaOH  =  NaCl  +  NaOCl  4-  H2O, 

is  practically  quantitative.  It  is  evident  that  only  50  per  cent 
of  the  chlorine  liberated  is  obtained  in  the  active  form  as  hypo- 
chlorite.  As  the  electrolysis  proceeds,  the  hypochlorite  becomes 
more  and  more  concentrated,  until  finally  a  limiting  concentra- 
tion is  reached,  whose  value  is  determined  by  a  number  of  factors, 
such  as  the  material  of  the  anode,  the  current  densities  on  the 
anode  and  cathode,  the  temperature,  and  the  original  concentra- 
tion of  the  chloride  solution.  This  is  due  to  the  fact  that  the 
hypochlorite,  almost  from  the  start,  is  also  decomposed  by  the 
current,  and  this  decomposition  increases  as  the  concentration 
of  the  hypochlorite  increases,  until  the  amount  decomposed  is 
just  equal  to  the  amount  produced.  This  decomposition  takes 
place  in  two  ways ;  at  the  cathode  the  hypochlorite  is  reduced 
by  the  hydrogen  as  follows : 

NaOCl  +  H2  =  H20  4-  NaCl,  (15) 

and  at  the  anode  the  hypochlorite  ion  is  liberated,  since  it  is 
more  easily  discharged  than  the  chlorine  ion,1  and  reacts  with 
the  water,  producing  chlorate  and  oxygen  according  to  the 
following  reaction : 2 

6  CIO-  +  3  H20  =  2  C103-  +  4  Cl-  +  6  H+  +  l£Oa.       (1Q) 

This  has  been  called  the  anode  chlorate  formation,  since  it  takes 
place  only  on  the  anode  and  not  throughout  the  solution. 

It  may  help  in  understanding  the  chloride  electrolysis  if, 
before  discussing  it  further,  a  method  of  analysis  is  explained 
which  has  been  extensively  used  in  the  study  of  this  subject 
for  following  the  reactions  taking  place  during  the  electrolysis. 

1  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  634,  (1902). 

2  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  667,  (1902).    This  equation  is  con- 
sidered fairly  well  established,  as  will  be  shown  below,  though  other  explanations 
of  the  results  are  possible. 


86  APPLIED    ELECTROCHEMISTRY 

This  consists  in  analyzing  the  gas  evolved  from  the  cell  and 
comparing  the  amount  of  hydrogen  and  oxygen  in  it  with  that 
evolved  by  the  same  current  from  a  water  coulometer.3  If  there 
is  less  hydrogen  from  the  chloride  cell  than  from  the  coulometer, 
the  difference  must  have  been  used  in  reducing  the  hypochlorite, 
according  to  equation  (15),  as  this  is  the  only  reducible  substance 
in  solution.  The  oxygen  in  the  gas  evolved  from  the  cell  con- 
taining the  chloride  solution  must  be  due  to  the  discharge  of  the 
hypochlorite  ion,  which  reacts  with  the  water  according  to  equa- 
tion (16),  producing  chlorate  and  oxygen.  Oettel  believed 
that  the  reaction  was  simply  the  evolution  of  oxygen  according 
to  the  equation : 

2  CIO-  +  H20  =  2  HOC1  +  i  02,  (IT) 

and  he  therefore  called  this  portion  of  the  current  loss  "  water 
decomposition,"  but  this  view  has  since  been  found  to  be  incor- 
rect. Since  the  proportion  of  oxygen  evolved  to  the  hypo- 
chlorite ions  discharged  is  the  same  in  either  case,  Oettel's 
calculations  will  not  be  changed,  but  the  explanation  of  the 
oxygen  evolution  will  be  given  by  equation  (16)  in  place  of 
(17).  According  to  equation  (17),  the  oxygen  evolved  is  pro- 
portional simply  to  a  current  loss  without  destroying  hypochlo- 
rite already  formed,  while  according  to  (16)  it  is  proportional  to 
a  fraction  of  the  current  that  changes  hypochlorite  to  chlorate. 

The  following  example,  illustrating  the  use  of  gas  analysis  for 
determining  the  yield  in  hypochlorite  as  the  electrolysis  pro- 
gr,esses,  is  taken  from  Oettel.3 

The  cell  containing  the  chloride  solution  was  connected  in 
series  with  a  water  coulometer.  During  a  given  time,  at  the 
beginning  of  the  electrolysis,  60  cubic  centimeters  of  gas  were 
evolved  from  the  coulometer  and  32  cubic  centimeters  from  the 
chloride  solution.  In  the  coulometer,  40  cubic  centimeters  of 
the  gas  must  have  been  hydrogen.  By  analysis  it  was  found 
that  the  gas  from  the  chloride  solution  had  the  following  com- 
position :  30  cubic  centimeters  of  hydrogen,  1.6  of  oxygen,  and 
0.4  of  chlorine.  This  shows  a  difference  in  the  amount  of  hy- 

*  I\  Oettel,  Z.  f.  Elektroch.  1,  354,  (1894). 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  87 

drogen  in  the  two  cells  of  10  cubic  centimeters.  This  amount 
must  therefore  have  been  used  to  reduce  the  hypochlorite 
already  formed.  Since  40  cubic  centimeters  of  hydrogen  repre- 
sents the  total  current,  or  100  per  cent,  the  loss  of  current  due 
to  reduction  was  100  x  |$  =  25  per  cent.  The  loss  due  to  the 

evolution  of  chlorine  equals  100  x  -1— ,  or  1  per  cent.     The  1.6 

cubic  centimeters  of  oxygen  are  equivalent  to  twice  as  much 
hydrogen,  or  3.2  cubic  centimeters.  The  loss  of  current  by 

o  n 

changing  hvpochlorite  to  chlorate  was  therefore  100  x  —  =  8 

40 

per  cent.  The  current  used  to  produce  hypochlorite  is  propor- 
tional to  the  amount  of  hydrogen  evolved  from  the  chloride 
solution,  diminished  by  the  quantity  of  chlorine  evolved,  and 
twice  the  amount  of  oxygen:  30  —  (3.2 -j- 0.4)=  26.4  cubic 
centimeters.  The  current  yield  is  therefore  100  x  J|  =  66  per 
cent.  This,  of  course,  means  that  66  per  cent  of  the  current 
produces  hypochlorite  according  to  equation  (5) : 

Cla  +  2  NaOH  =  NaCl  +  NaOCl  +  H2O. 

The  rest  of  the  current  destroys  hypochlorite  already  produced, 
or  produces  chlorine  which  escapes  from  the  cell.  Chlorine  is 
evolved,  however,  only  at  the  very  beginning  of  the  electrolysis, 
before  the  hydrate  and  chlorine  have  had  time  to  mix.  The 
following  table  sums  up  the  results  of  this  calculation : 

Current  used  to  produce  hypochlorite 66  per  cent 

Current  used  to  reduce  hypochlorite 25  per  cant 

Current  loss  by  changing  hypochlorite  to  chlorate      ....         8  per  cent 

Current  loss  due  to  evolution  of  chlorine       1  per  cent 

100  per  cent 

The  curves  in  Figure  24  4  will  illustrate  the  results  of  the  elec- 
trolysis of  a  neutral  4.37  normal  sodium  chloride  solution  with 
a  current  density  on  the  anode  of  0.075  ampere  per  square  centi- 
meter and  on  the  cathode  of  0.18  ampere  per  square  centimeter. 
The  electrolysis  was  continued  for  18  hours,  but  the  plots  are 
given  for  only  8  hours,  as  no  change  in  the  direction  of  the 

*  Miiller,  Z.  f.  anorg.  Ch.  22,  33,  (1900),  and  Z.  f.  Elektroch.  6,  14,  (1899). 


88 


APPLIED    ELECTKOCHEMISTRY 


FIG.  24.  —  Electrolysis  of  a  neutral,  4.37 
normal  sodium  chloride  solution 


curves  took  place  during  the  following  10  hours.     The  quanti- 
ties of  hypochlorite  and   chlorate  were    determined  by  direct 

analysis,  and  are  plotted  in 
terms  of  oxygen  contained  by 
each  in  grams  per  liter.  The 
corresponding  scale  of  ordi- 
nates  is  on  the  left.  The 
other  curves  were  obtained  by 
gas  analysis  as  described 
above.  The  scale  of  ordiiiates 
for  these  is  given  on  the  right, 
in  per  cent. 

It  will  be  seen  that  the 
fraction  of  the  current  used  in 
evolving  oxygen  and  for  re- 
duction, and  the  concentration 
of  the  hypochlorite  become 
constant  at  the  same  time. 
At  first  the  concentration  of  the  chlorate  remains  low,  but 
increases  steadily  as  soon  as  the  concentration  of  the  hypo- 
chlorite becomes  constant.  This  shows  that  hypochlorite  is 
the  first  product  of  the  electrolysis  and  that  it  is  the  starting 
point  for  the  formation  of  chlorate  ;  also  that  it  is  responsible 
for  the  evolution  of  oxygen,  as  would  be  expected  from  equa- 
tion (16). 

The  same  general  effect  is  produced  by  electrolysis  at  50°  C., 
except  that  the  concentration  of  the  hypochlorite  becomes  con- 
stant at  a  lower  value.  This  is  due  to  the  increase  in  the 
hydrolysis  of  the  chlorine  as  the  temperature  rises,  thus  pro- 
ducing a  greater  concentration  of  hypochlorite  ions  on  the 
anode  from  the  beginning.  The  quantity  of  hypochlorite  ions 
that  has  to  be  supplied  to  the  anode  from  the  solution  before 
they  are  discharged  is  therefore  less  than  at  a  lower  temper- 
ature; consequently  the  concentration  in  the  solution  will  not 
reach  as  high  a  value  as  in  the  cold  solution  before  the  amount 
of  hypochlorite  decomposed  equals  the  amount  produced.6 

6  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  364,  (1905). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES  89 

Both  the  reduction  of  the  hypochlorite  at  the  cathode  and 
the  discharge  of  the  hypochlorite  ion  on  the  anode  are  made 
more  difficult  by  increasing  the  current  density,  as  will  be  seen 
from  the  following  considerations.  The  greater  the  quantity 
of  chlorine  coming  from  the  anode,  the  more  it  tends  to  prevent 
the  hypochlorite  from  reaching  the  anode,  where  it  would  be 
discharged,6  and  the  smaller  the  cathode  is  made,  the  less  oppor- 
tunity will  the  hypochlorite  have  of  coming  in  contact  with 
nascent  hydrogen.  This  is  the  explanation  of  the  experimen- 
tal fact  that  increasing  the  current  density  on  the  cathode  low- 
ers the  reduction,  and  on  the  anode  it  makes  the  evolution  of 
oxygen  less  in  the  first  stages  of  the  electrolysis,  which  is  equiv- 
alent to  making  the  concentration  of  hypochlorite  attainable 
greater. 

In  a  dilute  solution  of  chloride,  the  maximum  hypochlorite 
concentration  is  less  than  in  a  concentrated  solution,  because  at 
a  given  concentration  of  chloride  the  hypochlorite  must  carry 
relatively  more  of  the  current  than  when  there  is  a  greater 
amount  of  chloride  present,  and  this  results  in  its  being  changed 
to  chlorate.  Table  10  illustrates  the  effects  of  temperature, 
current  density,  and  concentration  changes  on  the  electrolysis 
of  alkali  chloride  solutions. 

The  reduction  of  the  hypochlorite  can  be  nearly  entirely  pre- 
vented by  the  addition  of  a  small  amount  of  potassium  chro- 
mate  to  the  solution.6  Under  the  action  of  the  current  a  thin 
diaphragm  is  produced  that  gives  the  cathode  a  brownish  yel- 
low appearance  when  compared  with  a  fresh  piece  of  platinum, 
and  which  gives  a  test  for  chromium  when  dissolved  in  nitric 
acid.7  This  diaphragm  is  probably  an  oxide  of  chromium, 
since  a  cathode  of  metallic  chromium  does  not  prevent  reduc- 
tion. Potassium  chromate  is  as  effective  with  a  low-current 
density  as  with  a  high  density.  The  curves8  in  Figure  25  show 
the  effect  of  adding  0.18  per  cent  of  chromate  to  a  solution  con- 

6  E.  Miiller,  Z.  f.  Elektroch.  5,  469,  (1899);  Imhoff,  German  Patent,  110,420, 
(1898). 

7  E.  Mtiller,  Z.  f.  Elektroch.  7,  401,  (1901). 

8  E.  Miiller,  Z.  f.  Elektroch.  5,  470,  (1899). 


90 


APPLIED    ELECTROCHEMISTRY 


taining  30  per  cent  of  sodium  chloride.  The  broken  lines  refer 
to  the  solution  without  the  chromate.  The  current  density 
on  the  anode  in  both  cases  was  0.075  ampere  per  square  centi- 
meter ;  on  the  cathode,  0.18  ampere.  The  temperature  was 
from  42°  to  50°  C. 


11X) 
80 
CO 

i 

40 
20 

0 

C 

\ 

V 

s*^ 

CURRENT 

YIELD 

r 

REDUCTION 

+   .+.- 

NN^ 

CURRENT 

YIELD 

-+ 

> 

|     , 

OXYGEN  EVOLUTION 

F 

H>s^P- 

OXYGEN  EVOLUTION 

»--»-- 

—  1- 

REDUCTION  1 

1 

4                  8                  12                 16                 20                24 

FIG.  25.  —  Electrolysis  of  sodium  chloride 

Full  lines  refer  to  solutions  containing  0.18  per  cent  chromate,  broken  lines  to  solutions  containing 

no  chromate 

When  potassium  chromate  is  added,  the  whole  loss  in  current 
will  therefore  be  due  to  oxygen  evolved  according  to  equation 
(16),  which  may  be  written  : 

6  CIO-  +  3  H2O  +  6  F  =  6  H+  +  2  C1O8-  +  4  Cl~  +  1J  O2 

But  12  equivalents  of  electricity  are  required  to  produce  6  equiv- 
alents of  hypochlorite,  according  to  equation  (5),  which  may  be 
written  : 

12  Cl-  +  12  F  +  12  NaOH  =  6  NaCl  +  6  NaOCl  +  6  H2O, 

while  6  equivalents  are  required  to  discharge  the  hypochlorite  ions 
required  by  (16).  If  as  much  hypochlorite  is  to  be  decomposed 
by  (16)  as  is  produced  by  (5),  it  is  evident  that  twice  as  much  of 
the  current  must  be  used  in  producing  hypochlorite  as  is  used  in 
changing  it  to  chlorate.  That  is,  f  of  the  current  produces  active 


ELECTROLYSIS    OF  ALKALI   CHLORIDES 


91 


oxygen  in  the  solution  and  -J  produces  free  oxygen,  at  the  same 
time  changing  the  active  oxygen  from  hypochlorite  to  chlorate, 
according  to  (16).  Therefore,  excluding  reduction  and  the  for- 
mation of  chlorate  by  equation  (7),  when  the  concentration  of 
the  hypochlorite  has  reached  a  maximum,  in  a  neutral  or  slightly 
alkaline  solution,  33.3  per  cent  of  the  current  will  be  used  to 
produce  free  oxygen,  and  66.7  per  cent  to  produce  active  oxygen 
in  the  solution.9  The  oxygen  evolution  can  never  be  greater 
than  33.3  per  cent  unless  the  concentration  of  the  solution  is 
small,  in  which  case  oxygen  would  be  evolved  by  the  discharge 
of  hydroxyl  ions.  Except  for  these  points,  this  relation  is  inde- 
pendent of  the  other  conditions  of  the  experiment,  such  as  tem- 
perature, current  density,  and,  within  certain  limits,  the 
concentration.  This  is  illustrated  by  the  results  in  Table  10,10 
column  5. 

TABLE  10 
Solution  :  4.8  Normal  NaCl  and  2  Grams  K2CrO4  per  Liter 


LIMITING  CONC.  OF  OXYGEN 
IN  NaClO.    GRM.  PER 

PER  CENT  OF  CURRENT  PRO- 

AiMPERES  PER 

100  c.c. 

DUCING  OXYGEN 

TEMPERATURE 

SQ.  CM.  ON 

ANODE 

Smooth 

Platinized 

Smooth 

Platinized 

Pt.  Anode 

Pt.  Anode 

Pt.  Anode 

Pt.  Anode 

13 

0.017 

0.34 

0.61 

33.3 

31.0 

13 

0.17 

0.68 

0.89 

30  to  33 

34.5 

50 

0.017 

0.17 

0.31 

30  to  31 

22.0 

50 

0.17 

0.42 

0.64 

30 

28.0 

The  Solution  Changed  to  One  1.7  Normal  NaCl  and  Containing  2  Grams  K2CrO4  per 

Liter 


13 

0.017 

0.28 

0.48 

34 

33.5 

13 

0.17 

0.47 

0.65 

32.5 

35 

50 

0.017 

0.15 

0.23 

33.5 

29  to  31 

50 

0.17 

0.35 

0.40 

33 

33  to  34 

75 

0.017 

0.09 

0.15 

34 

25  to  27 

75 

0.17 

0.25 

0.32 

35  to  36 

29 

9  Foerster  and  Miiller,  Z.  f.  Elektroch.  9,  199,  (1903). 
10  Foerster  and  Miiller,  Z.  f.  Elektroch.  9,  196,  (1903). 


92  APPLIED    ELECTROCHEMISTRY 

In  the  above  experiments,  when  the  oxygen  evolution  is  less 
than  33.3  per  cent,  hypochlorite  is  lost  by  the  secondary  forma- 
tion of  chlorate.  Columns  3  and  5  show  that  the  maximum 
concentration  of  hypochlorate  is  different  under  different  con- 
ditions, but  that  when  this  concentration  is  reached,  the  frac- 
tion of  the  current  used  in  oxygen  evolution  is  practically  the 
same  under  widely  differing  conditions. 

If  the  solution  of  sodium  chloride  is  made  acid  with  hydro- 
chloric acid  at  the  beginning  of  the  electrolysis,  the  first  effect 
of  electrolysis  is  to  decompose  the  acid  until  the  solution  be- 
comes nearly  neutral.10  There  always  remains  a  small  quantity 
of  the  free  acid  throughout  the  solution,  however,  liberating  free 
hypochlorous  acid,  which  oxidizes  the  hypochlorate  to  chlorate 
through  the  entire  solution,  according  to  equation  (7).  This 
gives  a  method  of  increasing  th&^  yield  in  chlorate  over  that 
attainable  in  neutral  or  alkaline  solutions,  in  which  it  has  been 
shown  above  that  the  maximum  yield  is  66.7  per  cent.  If, 
before  the  maximum  concentration  of  hypochlorite  has  been 
reached,  a  quantity  of  acid  is  added  to  the  solution  which  is 
equivalent  to  only  a  fraction  of  the  hypochlorite  in  the  solution, 
the  latter  is  completely  oxidized  to  chlorate.  Further  elec- 
trolysis produces  more  hypochlorite,  to  which  acid  may  again  be 
added,  producing  more  chlorate.11  By  this  means,  chlorate  can 
be  produced  on  smooth  platinum  electrodes  with  nearly  90  per 
cent  of  the  theoretical  current  yield.  In  place  of  adding  the 
requisite  amount  of  hydrochloric  acid  from  time  to  time,  the 
solution  may  be  kept  slightly  acid  by  the  addition  of  potassium 
acid  fluoride,  KHF12,  as  patented  by  the  Siemens  and  Halske 
Company,12  or  of  alkali  bicarbonate,  which  is  patented  by  the 
Aktiengesellschaft  vorm.  Schuckert  &  Co.13 

Oettel  found  in  his  early  experiments  that  adding  0.3  gram 
of  potassium  hydrate  to  100  cubic  centimeters  of  a  solution 
containing  20  grams  of  potassium  chloride  does  not  materially 
affect  the  result  of  the  electrotysis,  but  that  as  the  alkalinity  is 

n  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  13,  (1902). 

12  Foerster  and  Miiller,  Z.  f.  Elektroch.  10,  731,  (1904). 

13  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  12,  (1902). 


ELECTROLYSIS   OF   ALKALI   CHLORIDES 


93 


GRAMS  OF  N  a  O  H   PER  LITER 


FIG.  26.  —  Effect  of  alkalinity  on  the  elec- 
trolysis of  a  solution  of  sodium  chloride 


increased,  the  maximum  concentration  of  hypochlorite  becomes 
less,  and  the  principal  product  of  the  electrolysis  "is  chlorate 
and  free  oxygen.14  The  curves  in  Figure  26  15  show  the  quanti- 
ties of  chlorate  and  hypochlorife  produced  per  liter  by  electro- 
lyzing  for  one  hour  solutions 
containing  200  grams  of  so- 
dium chloride  and  varying 
quantities  of  sodium  hydrate 
in  one  liter.  The  ordinates 
are  grams  of  oxygen  per  liter 
contained  in  the  chlorate  or 
hypochlorite  of  the  solution, 
and  the  abscissae,  the  number 
of  grains  of  sodium  hydrate 
added  to  one  liter  of  the  solu- 
tion. The  current  density  on 
the  anode  was  0.04  ampere 
per  square  centimeter. 

This  reduction  in  the  hypo- 
chlorite concentration  and  increase  in  that  of  the  chlorate  with 
increasing  alkalinity  is  explained  as  follows :  The  reaction  by 
which  the  chlorate  is  formed  in  strongly  alkaline  solutions  is 
the  same  as  that  in  neutral  or  slightly  alkaline  solutions,  and  is 
given  in  equation  (16),  and  the  difference  produced  by  the 
strong  alkalinity  is  that  the  chloride  finds  hydroxyl  ions  with 
which  to  react  immediately  on  the  anode,  forming  hypochlorite. 
There  is  therefore  a  much  higher  concentration  of  hypochlorite 
immediately  on  the  anode  than  throughout  the  rest  of  the  solu- 
tion, and  consequently  its  discharge  and  the  production  of 
chlorate  take  place  when  the  concentration  throughout  the 
solution  is  very  low.16  When  the  alkalinity  is  further  in- 
creased, the  hydroxyl  ions  also  begin  to  be  discharged  and  the 
yield  in  chlorate  falls  below  66.7  per  cent,  which  accounts  for 
the  maximum  point  in  the  chlorate  curve. 

14  Z.  f.  Elektroch.  1,  474,  (1895). 

15  Miiller,  Z.  f.  Elektroch.  6,  20,  (1899)  ;  Z.  f.  anorg.  Ch.  22,  72,  (1900). 

16  Foerster  and  Miiller,  Z.  f.  Elektroch.  9,  182,  and  200,  (1903)  ;  also  Foerster, 
Elektrochemie  wasseriger  Losungeu,  p.  366,  (1905). 


94 


APPLIED   ELECTROCHEMISTRY 


Another  difference  in  the  electrolysis  of  strongly  alkaline 
solutions  is  the  effect  of  temperature.  Higher  temperature  in 
neutral  solutions  decreases  the  maximum  concentration  of  hypo- 

chlorite  obtainable,  but  in 
strongly  alkaline  solutions 
the  effect  of  temperature  is 
just  the  reverse,  as  shown  in 
the  curves  in  Figure  27. 15 
The  ordi nates  are  the  number 
of  grams  of  oxygen  contained 
in  the  hypochlorite  or  chlo- 
rate in  one  liter  of  a  solu- 
tion originally  containing  200 
grams  of  sodium  chloride  and 
40  grams  of  sodium  hydrate 
the  same  volume.  The 


40 

TEMPERATURE 


FIG.  27.  —  Effect  of  temperature  on  the 
electrolysis  of  an  alkaline  solution  of 
sodium  chloride 


111 


electrolyses  lasted  one  hour  each,  with  a  current  density  on  the 
anode  of  0.045  ampere  per  square  centimeter.  Increasing  the 
anode  current  density  tends  to  counteract  this  temperature 
effect.  From  the  explanation  given  of  these  curves17  it  does 
not  seem  that  the  effect  of  temperature  in  strongly  alkaline 
solutions  is  thoroughly  understood. 

The  Electrolysis  of  Alkali  Chlorides  with  Platinized  Platinum 

Anodes 

Lorenz  and  Wehrlin  1  showed  that  the  use  of  a  platinized 
platinum  anode  increases  the  maximum  concentration  of  hypo- 
chlorite, and  that  the  oxygen  evolution  and  the  production  of 
chlorate  do  not  begin  at  a  time  when,  on  smooth  platinum, 
under  the  same  conditions  of  the  experiment,  the  oxygen  evolu- 
tion would  be  considerable.  When  the  electrolysis  is  continued 
for  a  longer  time,  however,  oxygen  evolution  and  chlorate  for- 
mation begin  just  as  on  smooth  platinum  anodes,  and  according 
to  the  same  reaction.2  The  only  difference  is  that  a  higher 

17  Foerster  and  Muller,  Z.  f.  Elektroch.  9,  205,  (1903) 

1  Z.f.  Elektroch.  6,  437,  (1900). 

2  Foerster  and  Muller,  Z.  f.  Elektroch.  8,  515,  (1902). 


ELECTROLYSIS    OF   ALKALI   CHLORIDES 


95 


i 

£4 


80 


==»= 


GO 


40 


concentration  of  hypochlorite  is  produced  before  the  quantity 
decomposed  in  a  given  time  is  equal  to  that  produced.  This  is 
illustrated  by  the  curves  in  Figure  28,  obtained  with  a  5.1 
normal  solution  of 

10 1 J 4-        I L^     c/,T~l 1 1  100 


sodium  chloride,  con- 
taining 2  grams  of 
potassium  chromate 
per  liter.2  The  brok- 
en curves  were  ob- 
tained with  a  smooth 
platinum  anode,  the 
solid  curves  with  a 
platinized  anode. 
The  ordinates  on  the 
right  give  the  per 
cent  of  the  current 
yield  and  the  per 
cent  of  the  current 
used  for  the  evolu- 
tion of  oxygen,  while 
on  the  left  the  ordi- 
nates give  the  num- 
ber of  grams  per  liter  of  oxygen  in  the  form  of  chlorate  and 
hypochlorite.  The  current  density  on  the  anode  was  0.067 
ampere  per  square  centimeter.  An  explanation  of  the  higher 
concentration  of  hypochlorite  obtained  with  platinized  anodes 
will  be  given  below  in  discussing  potentials  and  decomposition 
points. 


FIG.  28.  — The  electrolysis  of  a  5.1  n.  sodium  chloride 
solution,  containing  2  grams  of  potassium  chro- 
mate per  liter 

Dotted  lines  refer  to  smooth  platinum  anode,  full  lines  to 
platinized  platinum  anode 


The  Electrolysis  of  Alkali  Chlorides  on  Carbon  Anodes 

All  carbon  electrodes  are  more  or  less  porous ;  that  portion 
of  their  entire  volume  which  consists  of  pores,  or  the  porosity, 
varies  from  11.2  to  27.8  per  cent  for  different  kinds  of  carbon. 
For  Acheson  graphite  the  porosity  is  22.9  per  cent.1  The 
porosity  is  calculated  from  the  true  and  the  apparent  densities. 


1  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  372,  (1905). 


96  APPLIED   ELECTROCHEMISTRY 

The  apparent  density  b  is  the  weight  of  one  cubic  centimeter  of 
the  material,  while  the  true  density  a  is  the  weight  divided  by 
the  volume  actually  occupied  by  the  material.  The  value  of  a 
is  determined  by  mixing  bromoform  and  chloroform  in  such 
proportions  that  small  pieces  of  the  carbon  will  neither  sink  nor 
float  when  saturated  with  the  mixture.2  The  density  of  the 
mixture  is  then  determined  by  any  of  the  well-known  methods, 
and  thus  gives  that  of  the  carbon  directly.  The  value  of  the 

porosity  is  then  100—    -  per  cent. 

On  dipping  a  carbon  electrode  into  a  solution,  the  pores  become 
filled  with  the  solution,  and  the  solution  contained  in  the  electrode 
is  electrolyzed  as  well  as  that  on  the  surface  ;  but  since  the  dis- 
solved salt  cannot  be  replaced  in  the  pores  as  rapidly  as  in  the 
solution  on  the  surface  of  the  electrode,  where  stirring  replaces 
the  salt  decomposed,  the  solution  contained  in  the  pores  becomes 
more  dilute  than  on  the  surface.  Consequently  the  evolution 
of  oxygen  and  the  production  of  chlorate  will  begin  sooner, 
and  the  maximum  concentration  of  hypochlorite  will  be  less 
than  on  a  platinum  electrode,  when  the  other  conditions  of  the 
experiment  are  the  same.3 

The  effect  of  changing  the  chloride  concentration  or  the 
anode  current  density  on  the  yield  of  hypochlorite  and  on  the 
maximum  concentration  attainable  with  carbon  anodes  is  in 
the  same  direction  as  with  platinum  electrodes. 

A  part  of  the  oxygen  liberated  oxidizes  the  carbon  to  carbon 
dioxide,  part  of  which,  remaining  in  the  solution,  makes  the 
solution  slightly  acid,  and  therefore  changes  the  hypochlorite  to 
chlorate  by  equation  (16).  The  formation  of  carbonic  acid 
takes  place  in  solutions  at  20°  only  to  a  small  extent  and  after 
several  hours,  but  at  60°  it  begins  at  once,  and  the  total  quantities 
contained  in  the  gases  evolved  and  dissolved  in  the  solution 
amount  to  as  much  as  27  per  cent  of  the  amount  that  would  be 
produced  if  this  were  the  only  product  on  the  anode  of  the 
electrolysis.4 

2  Zellner,  Z.  f.  Elektroch.  5,  450,  (1899). 

8  L.  Sproesser,  Z.  f.  Elektroch.  7,"  1083,  (1901). 

*  Z.  f.  Elektroch.  7,  944  and  1014,  (1901). 


ELECTROLYSIS   OF   ALKALI   CHLORIDES  97 

Carbon  anodes  are  also  subject  to  mechanical  destruction,  due 
to  crumbling,  and  in  some  kinds  of  carbon  this  may  exceed  the 
loss  due  to  chemical  action. 

The  solution  in  the  pores  of  the  carbon  may  eventually  be- 
come so  dilute  that  hydroxyl  ions  are  discharged,  causing  the 
production  of  hydrochloric  acid  around  the  anode  ;  for  hydrogen 
ions  are  left  behind  by  the  discharge  of  hydroxyl  ions  and,  com- 
ing in  contact  with  chlorine  ions  migrating  from  the  anode, 
form  hydrochloric  acid.  This  fact  will  be  shown  later  to  be 
of  some  practical  importance. 

Acheson  graphite  has  been  found  to  last  better  in  the  elec- 
trolysis of  chlorides  than  any  other  kind  of  carbon.1 


The  Maximum  Concentrations  of  Hypo  chlorite  and  the  Maxi- 
mum Current  and  Energy  Yields  of  Hypochlorite  and 
Chlorate 

From  what  has  preceded,  it  will  be  evident  that  the  best 
conditions. for  obtaining  a  high  concentration  in  hypochlorite 
are  to  have  a  neutral,  concentrated  chloride  solution,  a  low  tem- 
perature, platinized  anodes,  and  to  prevent  reduction  by  potas- 
sium chromate.  Column  4  in  Table  11  shows  the  maximum 
amount  of  hypochlorite  obtainable  under  different  conditions 
of  the  experiment.1  The  values  given  in  grams  of  oxygen  may 
be  changed  to  grams  of  chlorine  by  multiplying  the  former  by 

5^4^  =  2:22.2     The  solution  was  4.79  normal  with  respect  to 
16 

sodium  chloride  and  contained  2  grams  of  potassium  chromate 
per  liter.  In  the  last  experiment  the  solution  was  only  1.73 
normal.  Both  electrodes  were  platinized.  • 

Since  the  decomposition  value  of  a  concentrated  solution  of 
sodium  chloride  on  either  smooth  or  platinized  platinum  is  2.2 
volts,  the  minimum  amount  of  energy  necessary  to  produce 

1  Foerster  and  Muller,  Z.  f.  Elektroch.  8,  10,  (1902). 

2  Foerster  and  Muller  use  the  ratio  4.44,  which  is  the  ratio  of  the  chemical 
equivalence  of  the  chlorine  and  oxygen  contained  in  hypochlorite.     The  ratio  of 
the  weights  contained,  however,  is  2.22. 


98 


APPLIED   ELECTROCHEMISTRY 


one  gram  of  oxygen  in  the  form  of  hypochlorite  is  7.4  watt 
hours.  From  the  table  it  is  evident  that  with  the  lowest 
current  density  this  value  is  very  closely  approached. 


TABLE  11 


GKAMS  PER  LITER 

CENTIGRADE 

PEK  SQ.  CM. 

VOLTS 

Of  0,  in 

OfCljin 

YIELD  IN 

PER  GRAM  02  IN 

DEOBEES 

ON  ANODE 

Hypochlo- 

Hypochlo- 

PER CENT 

HYPOCHLORITE 

rite 

rite 

13 

0.017 

2.40 

4.20 

9.3 

96 

8.4 

13 

0.017 

2.40 

5.24 

11.6 

90 

8.95 

10 

0.07 

3.10 

6.8 

15.0 

96 

10.84 

13 

0.17 

3.6 

5.28 

11.7 

99 

12.2 

13 

0.17 

3.6 

8.7 

19.8 

87 

13.5 

14 

0.17 

4.7 

5.20 

11.5 

95 

16.6 

If  chlorate  is  produced  entirely  secondarily  by  acidifying  the 
solution  from  time  to  time,  no  energy  is  required  for  its  forma- 
tion beyond  the  7.4  watt  hours  necessary  for  the  production  of 
the  hypochlorite.  By  working  in  this  way  and  by  using  plati- 
nized electrodes,  an  average  current  yield  of  98  per  cent  was 
obtained  in  a  run  in  which  3.66  volts  were  applied  to  the  cell.3 
This  is  12.5  watt  hours  per  gram  of  oxygen  in  the  form  of 
chlorate.  The  current  density  was  0.117  ampere  per  square 
centimeter.  By  reducing  the  current  density  the  theoretical 
value  of  7.4  watt  hours  could  of  course  be  more  nearly 
approached. 

The  Production  of  Per  chlorates 

A  perchlorate  is  a  more  stable  compound  than  a  chlorate,  since, 
as  is  well  known,  a  chlorate  on  heating  first  breaks  up  into 
perchlorate,  chloride,  and  oxygen,  according  to  the  equations :  * 

2  KC1O8  =  2  KC1  +  3  O2,  (18) 

4  KClOg  =  3  KC1O4  +  KC1.  (19) 

«  Foerster  and  Mtiller,  Z.  f.  Elektroch.  8,  16,  (1902). 

1  Roscoe  and  Schorlemmer,  Treatise  on  Chemistry,  1,  235,  (1905). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES  99 

A  solution  of  chloric  acid  is  also  unstable  when  its  concentra- 
tion exceeds  a  certain  value,  and  breaks  up  as  follows : 2 

2  HClOg  =  HC104  +  HC102.  (20) 

The  chloric  and  chlorous  acids  then  react  according  to  the  fol- 
lowing reversible  reaction  : 

HC103  +  HC102  ^±  H20  +  2  C102.  (21) 

These  reactions  are  similar  to  those  by  which  hypochlorous 
acid  breaks  up, 

3HC1O  =  HC1O3+2HC1, 
HC1O  +  HC1  ^±  Cl2  +  H2O. 

Perchlorates  are  produced  in  a  purely  chemical  way  only  by 
the  breaking  up  of  a  chlorate,  and  not  by  direct  oxidation. 

The  electrolytic  production  of  perchlorate  and  of  perchloric 
acid  was  discovered  by  Count  Stadion3  in  1816,  but  the  way 
in  which  this  oxidation  takes  place  was  not  understood  until 
recently.  This  is  not  a  direct  oxidation  of  chlorate  to  per- 
chlorate, as  would  be  expressed  by  the  equation  : 

ClOg-  +  2  OH-  +  2  F  =  ClO^  +  H2O, 

but  is  due  to  the  discharge  of  the  chlorate  ions  and  their  sub- 
sequent reaction  with  water,  as  follows  : 4 

2  C103-  +  H20  +  2  F  =  HC104  +  HC1O2  +  O.       (22) 

The  oxygen  does  not  escape,  but  oxidizes  the  chlorous  acid 
back  to  chloric  acid : 

HC1O2  +  O  =  HC103.  (23) 

The  principal  facts  concerning  the  production  of  perchlorate 
are  :  (1)  If  the  concentration  of  the  chlorate  is  over  8  per  cent, 
a  change  in  its  concentration  has  no  appreciable  effect  on  the 
current  yield ;  (2)  the  yield  increases  with  increasing  current 
density;  (3)  the  yield  falls  with  increasing  temperature; 
(4)  platinizing  the  anode  decreases  the  yield  and  (5)  in 

2  Oechsli,  Z.  f.  Elektroch.  9,  807,  (1903). 

3  Gilbert's  Ann.  52,  218,  (1816). 

4  Oechsli,  I.e.,  p.  819. 


100  APPLIED    ELECTROCHEMISTRY 

electrolyzing  alkali  chlorides,  perchlorate  is  not  produced  until 
nearly  all  of  the  chloride  has  been  changed  to  chlorate. 

In  an  acid  or  neutral  chlorate  solution,  perchlorate  can  be 
produced  with  a  high  current  yield,  as  Table  12  shows,  giving 
the  results  of  an  experiment  in  which  66  per  cent  sodium 
chlorate  solution  was  electrolyzed  with  a  smooth  platinum 
anode  on  which  the  current  density  was  0.083  ampere  per 
square  centimeter.  The  temperature  was  9°  C. 

TABLE  12 


TIME  IN  MINUTES  FROM  BEGINNING 
OF  ELECTROLYSIS 

CURRENT  YIELD  PER  CBNT 

5 

96.4 

20 

99.5 

35 

99.9 

180 

99.9 

210 

99.8 

300 

99.1 

Alkalinity  prevents  the  formation  of  perchlorates ;  the  cur- 
rent yield  falls  to  16  per  cent  for  a  solution  0.242  normal  with 
respect  to  sodium  hydrate,  with  the  same  current  density  as  in 
the  experiment  above.  This  is  probably  due  to  the  smaller 
number  of  chlorate  ions  that  are  liberated  as  the  alkalinity  is 
increased,  furnishing  hydroxyl  ions  that  are  more  easily  dis- 
charged than  the  chlorate.  An  increase  in  the  current  den- 
sity would  be  expected  to  counteract  this  effect  of  the  alkali, 
and  experiment  shows  that  it  does.  The  lower  yield  with 
platinized  anodes  is  due  to  the  lower  current  density  produced 
by  the  larger  surface. 

The  reduction  in  the  yield  by  an  increase  in  the  temperature 
is  supposed  to  be  due  to  the  greater  concentration  of  hydroxyl 
ions  of  water  from  the  increase  in  the  dissociation  with  the 
temperature. 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  101 

The  Electrolysis  of  Alkali  Chlorides  with  a  Diaphragm 

If  the  object  in  electrolyzing  an  alkali  chloride  is  to  produce 
an  alkali  hydrate  and  chlorine,  the  anode  and  cathode  must  be 
separated  in  order  to  prevent  the  hydrate  and  chlorine  from 
mixing.  There  are  four  ways  in  which  the  separation  of  the 
hydrate  and  chlorine  is  effected.  These  are:  (1)  by  the  use  of 
a  diaphragm  ;  (2)  by  inclosing  the  anode  in  an  inverted,  non- 
conducting bell,  with  the  cathode  outside  ;  (3)  by  charging  a 
mercury  cathode  with  sodium  in  an  electrolytic  cell  and  decom- 
posing the  sodium  amalgam  with  water  in  another  vessel  ;  and 
(4)  by  a  mercury  diaphragm,  which  acts  as  an  intermediate 
electrode. 

(1)  Since  electrolytic  conduction  takes  place  through  a  dia- 
phragm, it  is  evident  that  the  separation  in  this  case  will  not 
be  perfect,  for  the  diaphragm  prevents  only  mechanical  mixing. 
The  hydroxyl  ions  will  migrate  through  the  diaphragm  and 
react  with  the  chlorine  in  the  same  way  as  described  above. 
The  hydroxyl  ions  also  pass  through  the  diaphragm  by  ordi- 
nary diffusion.  Electro-osmosis,  on  the  other  hand,  drives  the 
liquid  through  the  diaphragm  from  the  anode  to  the  cathode, 
and  therefore  opposes  the  diffusion  and  migration  of  the 
hydroxyl  ions.1 

If  diffusion  and  osmosis  just  balance  each  other,  the  yield  in 
hydrate  can  be  calculated  as  follows.1  Before  sodium  hydroxide 
appears  at  the  diaphragm,  the  sodium  chloride  transports  all 
of  the  electricity,  but  when  the  hydrate  is  mixed  with  the 
chlorine,  the  hydrate  will  also  take  part  in  carrying  the  current 
through  the  diaphragm.  If  the  fraction  of  the  current  carried 
by  the  hydrate  is  x,  that  carried  by  the  chloride  will  be  1  -  x, 
and  x  and  1  —  x  must  be  proportional  to  the  conductivities  of 
the  hydrate  and  of  the  chloride  in  the  solution.  If  L±  is  the 
conductivity  of  the  chloride  and  L2  that  of  the  hydrate,  this  is 
expressed  by  the  equation  : 

1  —  X 


1  Foerster  and  Jorre,  Z.  f.  anorg.  Ch.  23,  158,  (1899). 


102  APPLIED   ELECTROCHEMISTRY 

in  which  c±  and  c2  are  the  concentrations  in  moles  per  liter,  ax 
and  «2  are  the  dissociations,  and  A/oc  and  X"oc  are  the  conduc- 
tivities at  infinite  dilution,  of  the  chloride  and  hydrate  respec- 

X' 
tively.     For  potassium  chloride  and  potassium  hydrate,  —^—  = 

A  <x 

0.545,  and  for  sodium  chloride  and  sodium  hydrate,  the  value 
of  this  fraction  is  0.502.  For  potassium  chloride  and  potas- 
sium hydrate,  equation  (24)  becomes 

1=      =  0.545^, 


or 

(25) 


+  0.545 


, 

1 


and  for  sodium  hydrate  and  sodium  chloride, 


x"  =  -  -  -  .  (26) 

1  +  0.502^ 


Now  if  all  of  the  current  were  carried  by  the  hydrate,  and  if 
n  were  its  transference  number,  n  equivalents  of  hydrate  would 
pass  out  of  the  cathode  compartment  through  the  diaphragm  in 
the  same  time  that  one  equivalent  is  produced.  In  this  case 
the  yield  in  hydrate  would  be 

A  =  100  (1  -  n)  per  cent. 

The  hydrate  carries  only  a  fraction  of  the  current,  however, 
equal  to  x.  The  yield  is  therefore 

A  =  100  (1  —  nx)  per  cent. 

The  transference  number,  w,  for  potassium  hydrate  is  0.74,  and 
for  sodium  hydrate  it  is  0.83.2  Substituting  the  values  for  x 
in  equations  (25)  and  (26),  and  the  values  for  n  just  given,  for 
potassium, 


ioo    -          °'74 


1  +  0.545  ^3 
3  Foerster,  Elektrochemie  wasseriger  Losungen,  p.  400,  (1905). 


(27) 


ELECTROLYSIS    OF   ALKALI    CHLORIDES  103 

and  for  sodium, 

__mn  °-83      _l 

(28) 


1+0.502 


It  is  evident  from  these  equations  that,  as  the  hydrate  becomes 
more  concentrated,  the  fraction  in  the  parenthesis  becomes 
greater,  which  reduces  the  value  of  A.  Table  13  shows  how 
the  yield  decreases  as  the  concentration  increases.3  The  elec- 
trolysis was  carried  out  with  700  cubic  centimeters  of  a  solution 
containing  200  grams  of  potassium  chloride  per  liter  in  the 
cathode  compartment,  and  500  cubic  centimeters  of  the  same 
solution  in  the  anode  compartment.  The  electrodes  were  plati- 
num, and  the  diaphragm  was  of  Pukal  clay.  The  current 
density  on  the  diaphragm  was  0.016  ampere  per  square  centi- 
meter. The  yield  which  was  being  obtained  at  the  end  of  each 
period  was  calculated  by  formula  (27)  from  the  values  of  the 
concentrations  of  chloride  and  hydrate  existing  at  the  end  of 
the  period,  assuming  that  the  dissociation  of  the  hydrate  and 
chloride  are  equal. 

TABLE  13 


EQUIVALENTS  PER 

TIME 

GRAMS  OF 
KOH  PRO- 
DUCED 

GRAMS  Cu 

DEPOSITED   IN 
COULOMETER 

MEAN  CURRENT 
YIELD  FOR  THE 
CORRESPONDING 

LITER  IN  THE 
CATHODE  COM- 
PARTMENT OF 

COMPUTED 
CURRENT 
YIELD 

Chloride 

Hydrate 

1st  2  hrs. 

17.78 

11.47 

88.08 

2.382 

0.418 

81.3 

2d  2  hrs. 

14.29 

11.71 

69.30 

2.224 

0.754 

70.4 

3d  2  hrs. 

13.60 

11.61 

66.50 

2.096 

1.071 

62.6 

4th  2  hrs. 

11.11 

11.85 

58.02 

2.066 

1.331 

55.0 

It  will  be  seen  from  the  numerical  values  in  equations  (27) 
and  (28)  that  the  yield  of  hydrate  with  potassium  chloride  will 
be  better  than  with  sodium  chloride,  at  18  °,  to  which  temperature 
these  numbers  apply.  Since,  however,  all  transference  numbers 
approach  the  limit  0.5  as  the  temperature  is  raised,  these  formulae 
indicate  that  the  yield  in  hydrate  would  increase  with  the  tem- 
»  Foerster  and  Jorre,  Z.  f.  anorg.  Ch.  23,  193,  (1899). 


104 


APPLIED   ELECTROCHEMISTRY 


perature  and  approach  the  same  value  for  sodium  and  potassium 
chlorides.  Since  a  rise  in  the  temperature  also  increases  the 
diffusion,  the  increase  in  the  yield  which  would  be  predicted  by 
the  formula  would  be  somewhat  too  large.3 

Since  the  hydroxyl  ions  that  migrate  to  the  anode  compart- 
ment find  an  excess  of  chlorine,  hypochlorous  acid  will  be  pro- 
duced according  to  equation  (2)  : 

C12  +  OH-  =  HOC1  +  C1-. 

If  this  proceeded  indefinitely,  the  loss  in  chlorine  would  be  twice 
the  loss  in  hydrate.  On  platinum  anodes  this  has  been  found  to 
be  true  in  the  first  stages  of  the  electrolysis.  As  the  hypochlo- 
rous acid  becomes  more  concentrated,  compared  to  the  chlorine, 
it  will  be  neutralized  by  the  hydroxyl  ions  coming  through  the 
diaphragm,  forming  hypochlorite.  This  is  then  immediately 
oxidized  to  chlorate  by  the  excess  of  hypochlorous  acid,  accord- 
ing to  equation  (7).  Consequently,  no  hypochlorite  is  found 
in  the  anode  compartment. 

The  process  in  the  anode  compartment  is  essentially  the  same 

when  carbon  anodes  are 
substituted  for  platinum, 
with  the  exception,  of 
course,  that  carbon  dioxide, 
as  well  as  oxygen,  is  pro- 
duced. 

(2)  The  principle  of  the 
bell  process  is  illustrated  in 
Figure  29.  The  anode  is 
placed  in  a  bell  and  the 
cathode  outside.  The  cur- 
rent flows  under  the  lower 
rim  of  the  bell  from  anode 

to  cathode.  Chlorine  is  evolved  and  passes  out  through  the 
tube  in  the  top  of  the  bell,  while  hydrate  is  formed  on  the 
cathode.  The  process  that  takes  place  in  this  cell  is  very  simi- 
lar to  that  in  a  cell  with  a  diaphragm.4  At  first  the  solution 


Fio.  29.  —  Bell  process 


4  Gustav  Adolph,  Z.  f.  Elektroch.  7,  581,  (1901). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES  105 

in  the  anode  compartment  is  divided  into  three  sharply  denned 
layers,  the  upper  one  saturated  with  chlorine,  next  to  this  a 
layer  of  unchanged  chloride,  and  below  this  a  layer  containing  a 
large  number  of  hydroxyl  ions.  The  hydroxyl  ions  migrate 
towards  the  anode,  and  on  coming  in  contact  with  an  excess  of 
chlorine  react  in  the  same  way  as  when  a  diaphragm  is  used. 

With  carbon  anodes  in  the  bell  process,  a  much  higher 
hydrate  concentration  can  be  obtained  without  destroying  the 
middle  layer  of  the  neutral  solution  separating  the  chlorine 
from  the  hydroxide;  at  the  same  time,  however,  the  current 
yield  is  less  than  the  theoretical.  This  is  due  to  the  fact  that 
free  oxygen  is  always  evolved  on  carbon  anodes,  producing  free 
hydrochloric  acid.  The  hydrogen  ions  from  this  acid  migrate 
towards  the  cathode  and  neutralize  the  hydroxyl  ions  migrating 
towards  the  anode,  and  thus  prevent  their  coming  in  contact 
with  free  chlorine.  In  consequence  of  this,  much  more  highly 
concentrated  solutions  of  hydrate  can  be  produced  by  the  bell 
process  with  the  same  energy  yield  than  by  the  diaphragm 
process.5 

In  actual  practice  the  bell  process  is  always  carried  out  with 
a  circulating  electrolyte.  Fresh  chloride  solution  flows  into 
the  anode  compartment,  where  it  must  be  spread  out  uniformly 
over  the  entire  area  of  the  bell,  so  that  the  neutral  layer  will 
not  be  disturbed. 

In  the  bell  process  the  losses  of  chlorine  and  hydrate  are 
equal,  so  that  the  current  yields  in  chlorine  and  hydrate 
must  also  be  equal.  The  chlorine  dissolved  in  the  anode  solu- 
tion is  carried  through  the  neutral  layer  by  circulation  and  is 
changed  to  hypochlorite  on  coming  in  contact  with  the  hydroxyl 
ions  below.  This  is  reduced  on  the  cathode,  producing  an 
equal  loss  in  hydrate.  The  loss  in  chlorine  at  the  anode  by 
the  evolution  of  oxygen  also  produces  an  equal  loss  in  hydrate, 
for  the  hydrochloric  acid  left  behind  by  the  oxygen  neutralizes 
an  equivalent  amount  of  hydrate.6 

With  a  circulating  electrolyte  a  current  yield  of  from  85  to 

5  Adolph,  I.e.  p.  589. 

6  Otto  Steiner,  Z.  f.  Elektroch.  10,  320,  (1904). 


106  APPLIED   ELECTROCHEMISTRY 

94  per  cent  can  be  obtained,  with  the  concentration  of  potassium 
hydrate  120  to  130  grams  per  liter,  and  the  chlorine  97  to  100 
per  cent  pure,  using  a  current  density  referred  to  the  area  of 
the  bell  of  2  to  4  amperes  per  square  decimeter,  and  from  3.7 
to  4.2  volts.7 

(3)  The  third  method  of  separating  the  hydrate  from  the 
chlorine  consists  in  depositing  the  metal  in  a  mercury  cathode, 
which  is  then  removed  from  the  cell  and  treated  with  water. 
The  sodium  or  potassium  reacts  with  the  water,  forming  the 
hydrate,  and  the  mercury  is  returned  to  the  cell  to  be  used  over 
again.     The  losses  in  this  process  are  due  to  the  recombination 
of  chlorine  dissolved  in  the  solution  with  the  alkali  metal  in  the 
amalgam,  and  to  the  reaction  of  the  alkali  metal  with  the  water 
before  leaving  the  electrolyzing  cell.     The  former  loss  may 
amount  to  100  per  cent  under  some  circumstances,  while  the 
loss  due  to  the  decomposition  of  water  is  small.8     In  order  to 
reduce  the  recombination  of  the  chloride  and  the  alkali  metal, 
the  current  density  on  the  cathode  should  be  high  and  also  the 
concentration  of  the  amalgam.     Strange  as  it  may  seem,  the 
potassium  amalgam  is  more  resistant  to  chlorine,  the  more  con- 
centrated it  is.     For  example,  increasing  the  concentration  of 
the  amalgam  from  0.012  per  cent  to  0.06  per  cent  increased 
the  yield  in  comparable  experiments  from  zero  to  90  per  cent. 
A  current  density  of  0.1  ampere  per  square  centimeter  gave  an 
88  per  cent  current  yield.     Since  the  principal  loss  is  due  to  a 
recombination  of  the  chlorine  and  the  alkali  metal,  the  yield 
will  be  the  same  for  both  alkali  and  chlorine.      If  the  amalgam 
is  covered  with  a  diaphragm  to  protect  it  from  the  chlorine, 
current  yields  of  98  per  cent  can  be  obtained.8 

(4)  The  fourth  method  of  separating  the  hydrate  from  the 
chlorine  consists  in  using  mercury  as  an  intermediate  electrode. 
The  principle  of  this  process  is  illustrated  in  Figure  30.     The 
electrolytic  cell  is  seen  to  consist  of  three  compartments ;  the 
two  outer  are  the  anode  compartments  containing  the  graphite 
anodes  AA,  and  the  middle  compartment  contains  the  cathode 

7  Z.  f.  Elektroch.  10,  330,  (1904). 

8  F.  Glaser,  Z.  f.  Elektroch.  8,  552,  (1902). 


ELECTROLYSIS  OF  ALKALI  CHLORIDES 


107 


(7,  consisting  of  an  iron  grid.  The  covers  of  the  anode  com- 
partments have  pipes,  not  shown  in  the  figure,  for  leading  off 
the  chlorine,  but  the  cathode  compartment  is  only  loosely  cov- 
ered, so  that  the  hydrogen  escapes  in  the  air. 

The  partitions  separating  the  compartments  do  not  quite 
reach  to  the  bottom  of  the  cell, 
but  the  opening  is  closed  by  a 
layer  of  mercury  covering  the 
bottom  of  the  cell.  The  alkali 
metal  is  electrolyzed  into  the 
mercury  in  the  anode  compart- 
ment and  is  electrolyzed  out  in 
the  cathode  compartment.  In 

the     Cathode     compartment    the     FIG.  30.  —  Cell  with  mercury  diaphragm 

amalgam  is  the  anode,  and  the 

alkali  metal  unites  with  the  hydroxyl  ions  liberated  on  it  and 
forms  hydrate.  In  order  to  stir  up  the  amalgam  so  that  the 
alkali  metal  will  get  into  the  cathode  compartment  as  soon  as 
possible,  the  whole  cell  is  slowly  tilted  back  and  forth,  causing 
the  mercury  to  flow  from  one  compartment  to  the  other. 

In  this  system  the  current  density  on  the  cathode  must  also 
be  at  least  0.1  ampere  per  square  centimeter.9  The  speed  of 
rocking  the  cell  also  affects  the  yield,  an  increase  in  the  rapidity 
decreasing  the  yield.  One  of  the  difficulties  encountered  in 
this  process  is  that  if  the  alkali  metal  becomes  too  dilute  in  the 
amalgam,  the  mercury  is  itself  oxidized  in  the  anode  compart- 
ment. To  avoid  this,  a  part  of  the  current  is  taken  directly 
from  the  mercury  by  a  shunt  circuit  in  which  there  is  a  suitable 
resistance  to  make  the  shunted  current  about  one  tenth  of  the 
total  current.  A  decrease  in  the  concentration  of  the  chloride 
solution  reduces  the  current  yield.  With  a  30  per  cent  potas- 
sium chloride  at  a  temperature  of  40°,  and  with  a  current 
density  of  0.1  ampere  per  square  centimeter,  Cantoni  obtained 
a  current  yield  in  hydrate  of  90  per  cent. 

»  Le  Blanc  and  Cantoni,  Z.  f.  Elektroch.  11,  611,  (1905).     . 


108  APPLIED   ELECTROCHEMISTRY 

Decomposition  Points  and  Potentials  of  Alkali  Chloride  /Solutions 

In  a  chloride  solution  before  electrolysis  there  are  only  the 
hydroxyl  and  chlorine  anions,  while  after  the  electrolysis  there 
are  also  hypochlorite  and  chlorate  anions.  The  cations  are 
the  alkali  metal  and  hydrogen  both  before  and  after  electrol- 
ysis. A  knowledge  of  the  potential  differences  between  anode 
and  solution  at  which  the  different  anions  are  discharged  will 
help  in  understanding  the  chloride  electrolysis. 

The  potential  difference  at  which  an  ionized  substance  is 
discharged,  or,  what  is  the  same  thing,  if  the  process  is  reversi- 
ble, the  potential  difference  produced  by  the  substance  when 
brought  in  contact  with  a  platinum  electrode,  is  dependent  on 
its  chemical  nature  and  on  its  concentrations  in  the  charged 
and  discharged  conditions.  Thus  the  potential  difference 
between  a  platinum  electrode  charged  with  chlorine  and  a 
chloride  solution  is 

T>  rji              Tf  /T                 n  rn\~  i~1 

-flJ-  i "'VcL  MJLl  i 7.     i    i VCL.  (^9^ 


where'  <7clj  is  the  concentration  of  free  chlorine  in  moles  per 
liter  surrounding  the  anode,  tfcl_  is  the  concentration  of  chlo- 
rine ions  in  the  solution,  and  k  is  a  constant.  If  <7C1  and  <7C1_ 

RT 

are  both  equal,  the  value  of  e  is  — -  log  k,  and  is  called  the 

electrolytic  potential.  For  a  solution  saturated  with  chlorine 
at  atmospheric  pressure  containing  0.064  mole  per  liter,  and 
normal  with  respect  to  chlorine  ions,  e  =  —  1.667  volts,1  assum- 
ing the  potential  of  the  dropping  electrode  to  be  zero.  The 
negative  sign  indicates  that  the  solution  is  negatively  charged. 
Chlorine,  cannot  therefore  be  liberated  at  atmospheric  pressure 
at  a  potential  difference  less  than  this  value.  On  a  platinized 
platinum  cathode  in  an  acid  solution,  normal  with  respect  to 
hydrogen  ions,  hydrogen  would  be  liberated  at  —  0.277  volt. 
But  the  solution  around  the  cathode  is  neutral  to  start  with, 
and  soon  after  the  electrolysis  has  begun  is  alkaline,  due  to  the 

i  Miiller,  Z.  f.  phys.  Ch.  40,  158,  (1902). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES 


109 


formation  of  alkali  hydrate.  The  hydrogen  ion  concentration 
is  then  very  much  reduced  below  its  value  in  the  original 
neutral  solution.  This  alkalinity  might  have  any  value,  but 
for  the  purpose  of  calculation  the  solution  around  the  cathode 
will  be  assumed  normal,  though  it  would  not  reach  such  a  high 
value  in  a  cell  not  containing  a  diaphragm.  The  value  of  the 
potential  of  the  cathode  on  tvhich  hydrogen  is  being  liberated 
would  then  be  0.54  volt,  0.82  volt  more  positive  than  the  po- 
tential in  a  normal  acid  solution.2  The  cell  would  then  have 
an  electromotive  force  of  its  own  of 

e  =  0. 54  -  (  -  1. 66)  =  2.20  volts. 

The  decomposition  point  of  a  concentrated  solution  of  sodium 
chloride,  determined,  as  usual,  with  a  very  small  current,  is 
1.95  volts,  but  this  is  because  the  solution  around  the  cathode 
is  more  nearly  neutral  than  assumed  above.  Continuous  elec- 
trolysis requires  from  2.3  to  2.1  volts.3 


1.6  1.8 

ANODE    POTENTIAL 


FIG.  31 .  —  Curves  showing  the  relation  between  current  and  anode  potential,  in 
solutions  of  sodium  chloride  and  of  sodium  hypochlorite 

As  was  shown  above,  when  the  hypochlorite  reaches  a  certain 
concentration,  the  hypochlorite  ion  is  also  deposited  on  the  anode. 
It  has  never  been  possible  to  determine  the  decomposition  point 
of  this  ion,  however.  It  is  evident  from  the  curves  in  Figure 
31,4  in  which  the  decomposition  points  of  two  solutions  are 

2  Le  Blanc,  Electrochemistry,  p.  209,  (1907). 

»  Lorenz,  Z.  f.  Elektroch.  4,  247,  (1897). 

*  Foerster  and  Muller,  Z.  f.  Elektroch.  8,  634,  (1902). 


110 


APPLIED    ELECTROCHEMISTRY 


given,  one  normal  with  sodium  hypochlorite  and  0.025  normal 
with  sodium  hydrate,  the  other  normal  with  sodium  chloride 
and  0.01  normal  with  sodium  hydrate,  that  hypochlorite  ions  are 
not  liberated  before  hydroxyl  ions.  This  is  shown  by  the  fact 
that  there  was  no  increase  in  the  current  below  the  potential 
—  1.16  volts,  approximately  the  point  at  which  hydroxyl  ions 
are  liberated  in  a  normal  hydrate  solution.  It  is  also  evident 
that  the  electrolysis  of  a  normal  chloride  solution  begins  at  a 
higher  potential  than  the  hypocholorite  solution.  The  decom- 
position point  of  the  hypochlorite  ion  therefore  lies  between 
those  of  the  hydroxyl  and  the  chlorine  ions. 

Since  there  is  a  difference  of  about  0.5  volt  between  the  de- 
composition points  of  chlorine  and  hydroxyl  ions,  it  would 
seem  impossible  to  liberate  chlorine  ions  in  a  strongly 
alkaline  solution.  This  would  be  the  case  if  it  were  not 
that  the  potential  of  an  anode  on  which  oxygen  is  liberated 
increases  continuously,  and  eventually  reaches  the  potential 
at  which  chlorine  is  liberated.  If  it  were  not  for  this  in- 
crease in  the  potential,  caused  by  the  liberation  of  oxygen,  the 
decomposition  of  a  chloride  in  an  alkaline  solution  would  be 
impossible.5  Another  effect  which  tends  to  make  chlorine  de- 
posit in  an  alkaline  solution  is  the  fact  that  the  hydrate  has  a 
depolarizing  effect  on  the  chlorine,  in  consequence  of  which 
chlorine  will  be  liberated  at  a  lower  potential  than  that  neces- 
sary for  its  deposition  at  atmospheric  pressure.  Table  14  shows 

TABLE  14 


PER  CENT  YIELD  IN  ACTIVE  OXYGEN 

POTENTIAL 

AMPEBES 

Total 

As  Hypo- 
chlorite 

As  Chlorate 

-1.09 

- 

1 

0.0 



-1.21  to  -1.27 

0.016 



0.9 



-  1.30  to  -  1.51 

0.28  to  0.14 

3.2 

2.6 

0.6 

-  1.51  to  -  1.595 

0.5    to  0.4 

16.4 

8.2 

8.2 

6  Foerster  and  Mtiller,  Z.  f.  Elektroch.  9,  184,  (1903). 


ELECTROLYSIS   OF   ALKALI   CHLORIDES 


111 


that  hypochlorite  and  chlorate  are  formed  in  a  solution  normal 
with  sodium  hydrate,  and  3.6  normal  with  sodium  chloride,  at 
an  anode  potential  below  —  1.667  volts,  the  potential  at  which 
chlorine  is  liberated  at  atmospheric  pressure.6  The  anode  was 
platinized  platinum,  of  14  square  centimeters  area. 

It  will  be  noticed  that  as  the  anode  potential  increases  in  nu- 
merical value,  the  proportion  of  chlorate  to  hypochlorite  in- 
creases. This  is  due  to  the  fact  that  the  hypochlorite  ions, 
which  are  more  easily  discharged  than  the  chlorine  ions,  are 
more  subject  to  deposition  as  the  potential  of  the  anode  in- 


1.1 


1.3     '  1.5  1.7  1.9  2.1 

ABSOLUTE  POTENTIAL  DIFFERENCE  BETWEEN  ANODE  AND  SOLUTION 


FIG.  32.  —  Curves  showing  the  relation  between  current  and  anode  potential  for 
smooth  and  for  platinized  platinum  anodes 

creases,  with  the  subsequent  production  of  chlorate  according 
to  equation  (16). 

On  smooth  platinum  anodes  the  potential  difference  during 
electrolysis  is  about  0.58  volt  greater  than  on  platinized  plati- 
num.7 The  decomposition  points  of  sodium  chloride  on  plati- 

e  Foerster  and  Miiller,  Z.  f .  Elektroch.  9,  183,  and  201,  (1903). 
7  Z.  f.  Elektroch.  6,  437,  (1900). 


112  APPLIED    ELECTROCHEMISTRY 

nized  platinum  and  on  smooth  platinum  anodes  shows  the  same 
difference,  as  is  seen  from  the  curves  in  Figure  32. 8  It  is  evi- 
dent that  the  overpressure  of  an  anion  is  a  function  not  only  of 
its  own  chemical  nature,  but  also  of  the  solution  from  which  it 
is  deposited,  of  the  current  density,  and  of  the  material  com- 
posing the  anode. 

The  cause  of  this  overpressure  of  0.58  volt  on  platinum  is  not 
well  understood;  it  may  be  due  to  the  resistance  of  a  film  of  gas 
liberated  on  the  anode.  There  is  a  corresponding  overvoltage 
in  other  solutions,  such  as  sodium  hydrate  and  sulphuric  acid, 
where  oxygen,  in  place  of  chlorine,  is  liberated.  These  over- 
pressures are  not  equal  for  the  same  current  density  in  these 
different  solutions.9 

Though  the  overpressure  on  smooth  platinum  anodes  may 
not  itself  be  understood,  its  presence  offers  a  possible  explanation 
of  the  higher  concentration  of  hypochlorite  obtained  with  a 
platinized  anode,  for  the  relation  between  the  decomposition 
potential  and  the  concentration  of  ions  is  that  the  decomposition 
potential  decreases  as  the  concentration  increases.  Therefore, 
with  a  lower  anode  potential,  the  concentration  of  the  hypo- 
chlorite ions  would  have  to  be  greater  before  decomposition 
takes  place.10 

It  is  an  experimental  fact,  as  has  been  stated  above,  that  very 
little  perchlorate  is  produced  until  most  of  the  chloride  has  been 
changed  to  chlorate.  This  is  due  to  the  fact  that  the  decom- 
position potential  of  normal  sodium  chlorate  is  2.36  volts,11  while 
that  of  the  chloride  is  1.95  volts.3  The  high  potential  re- 
quired for  the  deposition  of  the  chlorate  cannot  therefore  be 
reached  until  most  of  the  chloride  has  been  used  up. 

When  chlorine-  is  dissolved  in  water,  according  to  equations 
(2)  and  (4),  a  certain  amount  of  hypochlorous  acid  and  hypo- 
chlorite will  be  produced.  Both  hypochlorous  acid  arid  hypo- 
chlorite are  oxidizing  agents,  and  therefore  give  an  unattackable 

s  Miiller,  Z.  f.  Elektroch.  8,  426,  (1902). 

•  Foerster  and  Miiller,  Z.  f.  Elektroch.  8,  533,  (1902). 
i°  Foerster  and  Miiller,  Z.  f.  Elektroch.  9,  199,  (1903). 
11  Wohlwill,  Z.  f.  Elektrocb.  5,  52,  (1898). 


ELECTROLYSIS    OF  ALKALI   CHLORIDES  113 

electrode  a  definite  potential.     If  the  reactions  by  which  they 
give  off  oxygen,  or  what  is  the  same  thing,  hydroxyl  ions,  are 

HOC1  =  OH-  +  Cl-  +  2  F,  (30) 

CIO-  +  H2O  =  Cl-  +  2  OH  +  2  F,  (31) 

the  potentials  would  be  given  by  the  equations 
RT , 


(33> 


*  V    OH- 

and  for  equilibrium  concentrations, 


tfj  being  taken  from  equation  (29).     When  chlorine  is  liberated 
on  an  unattackable  anode,  the  equilibrium  represented  by  (9), 


=  3.6  x  IP"11    "ocl  =  1.4  xlO'17 


must  be  established,  and,  assuming  the  chlorine  electrode  is  re- 
versible, the  production  of  hypochlorite  and  hypochlorous  acid 
must  be,  according  to  (31)  and  (32),  taken  from  right  to  left. 
This  means  that  a  primary  production  of  hypochlorite  and 
hypochlorous  acid  takes  place  on  the  anode  to  a  small  extent. 

Fluorides,  Bromides,  and  Iodides 

The  electrolysis  of  the  other  alkali  halogen  compounds  has 
not  attained  anything  like  the  commercial  importance  of  the 
electrolysis  of  chlorides  ;  still,  for  the  sake  of  completeness,  the 
behavior  of  the  other  alkali  halides  on  electrolysis  will  be  briefly 
described. 

Fluorine  decomposes  water  with  the  evolution  of  oxygen  and 
ozone  : 

2  OH-  +  2  Fl-  =  H2O  +  O.  (35) 

No  oxygen  compounds  of  fluorine  are  known,  consequently  the 
electrolysis  of  fluorides  offers  nothing  to  compare  with  what 
is  obtained  in  the  case  of  chlorides. 


114  APPLIED   ELECTROCHEMISTRY 

Bromine  enters  into  exactly  similar  equilibria  when  added 
to  alkali  hydrate  to  those  already  described  in  the  case  of 
chlorine.  They  are  represented  by  the  equations  : l 

Br2  +  OH-  =  HOBr  +  Bi-1 
HOBr  +  OH-  =  BrO-  +  H2OJ ' 

Hypobromite  is  therefore  always  the  first  product  of  the  reac- 
tion when  bromine  acts  on  alkali  hydrate.  When  one  mole  of 
bromine  acts  on  one  equivalent  of  hydrate,  the  reaction  is  not 
as  complete  as  in  the  case  of  chlorine,  but  appreciable  quantities 
of  bromine  and  hydrate  remain  unchanged. 

The  formation  of  bromate  according  to  the  equation 

2  HOBr  +  NaBrO  =  NaBrO3  +  2  HBr  (37) 

takes  place  with  over  100  times  the  velocity  of  the  correspond- 
ing reaction  for  chlorate.  This  reaction  takes  place  even  in 
slightly  alkaline  solutions  with  a  high  velocity,  on  account  of 
the  greater  hydrolysis  of  hypobromite,  but  in  solutions  that  are 
at  least  0.1  normal  with  respect  to  hydrate,  the  hydrolysis  has 
been  so  far  reduced  that  hypobromite  is  as  stable  as  hypo- 
chlorite.  When  a  concentration  of  the  hydrate  is  still  further 
increased,  the  rate  at  which  bromate  is  produced  increases, 
probably  according  to  the  reaction  : 

3  NaBrO  =  NaBrO3  +  2  NaBr.  (38) 

This  differs  from  the  corresponding  reaction  for  chlorate,  in 
that  it  proceeds  with  scarcely  any  evolution  of  oxygen.  This 
reaction,  however,  is  very  much  slower  than  that  represented 
by  equation  (37),  and  need  not  be  considered  in  the  practical 
preparation  of  bromate. 

In  electrolyzing  a  bromide  solution,  free  bromine  is  liberated 
on  the  anode,  accompanied  by  oxygen  from  the  discharge  of 
hydroxyl  ions,  and  produces  hypobromite  with  the  hydrate 
formed  at  the  cathode.  The  concentration  of  the  hypobromite 
increases  up  to  a  certain  point,  after  which  it  remains  constant, 
and  the  only  product  of  the  electrolysis  is  then  bromate.  As 

i  Horst  Kretzschmar,  Z.  f.  Elektroch.  10,  789,  (1904). 


ELECTROLYSIS   OF  ALKALI   CHLORIDES  115 

the  hypobromite  increases  in  concentration,  the  evolution  of 
oxygen  also  increases,  the  hydroxyl  ions  for  which  are  fur- 
nished by  the  hydrolysis  of  the  hypobromite. 

Bromate  is  formed  partly  by  the  secondary  oxidation  of  hypo- 
bromite by  hypobromous  acid,  which  is  always  present  to  a 
certain  extent  on  the  anode,  and  partly  by  direct  oxidation 
according  to  the  equation  : 


(39) 

The  hypobromite  ion  is  not  discharged,  so  there  is  no  reaction 
between  it  and  water,  as  there  is  in  the  case  of  the  hypochlorite 
ion. 

The  concentration  of  hypobromite  attainable  is  greatest  with 
a  high  current  density,  a  high  concentration  of  bromide,  and  a 
low  temperature.  It  is  also  higher  on  platinized  anodes  than 
on  smooth,  as  is  the  case  with  hypochlorite.  The  highest  con- 
centration of  hypobromite  attainable  is  about  the  same  as  that 
of  hypochlorite,  but  the  current  yield  is  less,  on  account  of  the 
greater  tendency  to  form  bromate.  Unless  potassium  chro- 
mate  is  added  to  the  solution,  bromate,  as  well  as  hypobromite, 
is  subject  to  reduction  on  a  smooth  platinum  cathode,2  which 
is  another  point  of  difference  between  chlorate  and  bromate. 

Perbromic  acid  and  its  salts  cannot  be  produced  by  elec- 
trolysis, and  it  is  doubtful  whether  they  exist  at  all.3 

When  iodine  is  brought  in  contact  with  hydrate,  the 
equilibria 

I2+OH-=HOI  +  I-     1 

HOI  +  OH-  =  01-  +  H20  I 

are  established  exactly  as  in  the  case  of  chlorine  and  bromine.4 
Hypoiodite  is  very  considerably  hydrolyzed,  and  therefore, 
unless  the  solution  is  very  alkaline,  it  changes  rapidly  to  iodate 
by  the  reaction  : 

2  HOI  +  KIO  =  KIO3  +  2  HI.  (41) 

2  H.  Pauli,  Z.  f.  Elektroch.  3,  474,  (1897). 

8  Roscoe  and  Schorlemmer,  Treatise  on  Chemistry,  1,  358,  (1905). 

4  Foerster  and  K.  Gyr,  Z.  f.  Elektroch.  9,  1,  (1903). 


116  APPLIED    ELECTROCHEMISTRY 

If  an  excess  of  alkali  is  present,  however,  the  hydrolysis  is 
driven  back,  and  hypoiodite  can  be  obtained  free  from  iodate. 
The  formation  of  iodate  is  accelerated  by  an  increase  in  the 
temperature  and  concentration  of  the  iodide,  and  by  decreasing 
the  alkalinity. 

The  rapidity  with  which  hypoiodite  changes  to  iodate  is 
shown  by  the  following  facts :  If  50  cubic  centimeters  of  a 
0.1  normal  iodine  solution  are  mixed  with  50  cubic  centimeters 
of  a  normal  sodium  hydrate  solution  at  zero  degrees,  a  0.05 
normal  hypoiodite  solution  would  be  100  per  cent  yield.  Imme- 
diately after  mixing,  however,  there  is  only  95  per  cent  of  this 
amount  of  hypoiodite,  and  after  2  minutes,  only  75  per  cent 
remains.  On  dilution  it  is  more  stable  ;  a  0.01  normal  hypoio- 
dite solution  remains  practically  unchanged  for  a  few  minutes 
in  a  0.1  normal  alkaline  solution  at  room  temperature. 

On  electrolyzing  a  neutral  solution  of  alkali  iodide,5  the  io- 
dine liberated  on  the  anode  comes  in  contact  with  the  hydrate 
from  the  cathode,  and  the  first  product  is  hypoiodite.  This 
changes  over  to  iodate  rapidly,  as  shown  above,  even  in  an  alka- 
line solution,  so  that  the  electrolysis  of  an  alkali  iodide  solution 
is  similar  to  that  of  a  slightly  acid  chloride  solution.  Conse- 
quently the  hypoiodite  solution  reaches  a  limiting  concentra- 
tion, after  which  the  product  of  the  electrolysis  is  exclusively 
iodate.  This  limiting  concentration  of  hypoiodite  is  determined 
by  the  current  density,  temperature,  and  the  concentration  of 
iodide  and  alkali.  An  increase  in  the  alkalinity  increases  the 
limiting  concentration  of  the  hypoiodite,  while  it  decreases 
that  of  the  hypochlorite.  This  is  due  to  the  different  ways 
in  which  iodate  and  chlorate  are  formed  in  alkaline  solutions. 

As  the  hypoiodite  never  can  become  concentrated,  the  possi- 
bility of  the  electrolytic  discharge  of  the  hypoiodite  ion  is 
very  small.  Therefore  the  oxygen  evolution,  which  takes  place 
only  when  the  iodide  is  dilute  and  the  solution  is  alkaline, 
must  be  due  nearly  entirely  to  the  discharge  of  hydroxyl  ions. 
It  is  therefore  in  no  way  connected  with  the  formation  of  io- 
date. 

6  Foerster  and  Gyr,  Z.  f.  Elektroch.  9,  215,  (1903). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES 


117 


Periodates  cannot  be  produced  by  the  electrolysis  of  iodates 
except  with  a  diaphragm.6  This  is  shown  by  the  fact  that 
without  a  diaphragm  no  hydrogen  is  evolved  on  electrolysis, 
but  is  all  used  in  reducing  the  iodate.  After  electrolysis  has 
proceeded  a  while,  the  oxygen  evolution  also  becomes  zero. 
There  is  then  a  constant  amount  of  iodide  and  iodate  in  the 
solution  ;  as  fast  as  iodate  is  formed  on  the  anode,  it  is  reduced 
on  the  cathode.  In  neutral  solutions  iodate  is  not  oxidized  to 
periodate,  and  in  alkaline  solutions,  potassium  chromate  does 
not  prevent  the  reduction  of  iodate  to  iodide. 

By  using  a  diaphragm,  a  current  yield  in  periodate  of  about 
26  per  cent  can  be  obtained.  The  best  conditions  are  low  tem- 
perature, low-current  density,  and  at  least  4  per  cent  alkalinity. 


2.    TECHNICAL  CELLS  FOR  HYPOCHLORITE,  CHLORATE,  HY- 
DRATE, AND  CHLORINE 

Hypochlorite.  —  Hermite's  cell,  patented  in  1887,  was  the 
first  cell  to  be  even  moderately  suc- 
cessful for  the  electrolytic  manufac- 
ture of  hypochlorite.1  It  consisted 
of  a  rectangular  box  of  ceramic  with 
a  grooved  channel  around  the  top  for 
carrying  off  the  solution  of  sodium 
and  magnesium  chlorides,  which 
entered  at  the  bottom.  The  cathode 
consisted  of  numerous  disks  of  zinc 
supported  on  two  slowly  rotating 
shafts  running  through  the  box  and 
separated  from  each  other  by  a  parti- 
tion. The  anodes,  consisting  of  thin 
sheets  of  platinum  held  on  a  noncon- 
ducting frame,  were  placed  between 
the  zinc  disks.  In  practice  this  cell 


FIG.  33.  —  Elevation  of  Kellner 
cell 


6  E.  Muller,  Z.  f.  Elektroch,  7,  509,  (1901). 

1  W.  H.  Walker,  Electroch.  Ind.  1,  440,  (1903);  Engelhardt,  HypochJorite 
and  Elektrische  Bleiche,  p.  77,  (1903). 


118 


APPLIED   ELECTROCHEMISTRY 


g.ives  a  current  yield  of  about  40  per  cent  and  an  energy  yield 

of  one  kilogram  of  chlorine  for  twelve  kilowatt  hours.2 

The  Kellner  cell,  made  by  the  Siemens 
and  Halske  Company,  is  shown  in  Figures 
33,  34,  and  35.  A  glazed  stoneware  vessel 
is  divided  into  a  number  of  compartments 
by  glass  plates  fitted  into  grooves  in  the 
sides  of  the  cell.  The  plates  are  wound 
with  platinum -iridium  wire,  which  acts 
as  intermediate 

electrodes,  form-  [f]  [i  fj  H  H'H  \]  1}  fi  H] 

ing  the  anodes 
on  one  side  and 
the  cathode  on 
the  other  side  of 
of  the  glass  plates. 
The  solution 

enters  through  holes  in  the  bottom  of 

the  cell  and  the  electrolyzed  solution  flows  out  spouts  at  the 


FIG.    34.  —  Electrodes 
Kellner  cell 


© 


0 


a 


FIG.  35.  —  Plan  of  Kellner  coll 


FIG.  36.  —  Kellner  cell 


top  into  a  vessel  containing  a  cooling  coil.     From  here  it  is 
pumped  up  through  the  cell  again.     This  circulation  continues 


2  Engelhardt,  I.e.  p.  86. 


ELECTROLYSIS   OF   ALKALI   CHLORIDES 


119 


until  the  desired  strength  of  hypochlorite  has  been  obtained. 
This  is  illustrated  in  Figure  36. 

The  Schuckert  cell  is  also  made  by  the  Siemens  and  Halske 
Company.     It  is  made  of  stoneware  and  is  divided  into  eight 


FIG.  37.  —  Horizontal  section  of  Haas  aud  Oettel  cell 

or  ten  compartments,  each  having  two  graphite  cathodes  and  a 
Pt-Ir  foil  anode.  The  solution  enters  at  one  end  and  travels 
in  a  zigzag  direction  through  the  different  compartments.  Each 
cell  has  a  cooling  coil,  and  no  pumps  are  needed  for  circulation. 
The  units  are  built  in  pairs  and  are  designed  for  110  volts. 


120 


APPLIED   ELECTROCHEMISTRY 


The  Haas  and  Oettel  cell  is  shown  in  horizontal  and  vertical 
cross  sections  in  Figures  37  and  38. 3  The  electrolyzer  b  is  im- 
mersed in  the  solution  in  the  storage  vessel  a.  The  electrolyzer 
consists  of  a  vessel  divided  into  several  compartments  c  by 
divisions  r,  made  of  carbon  or  any  suitable  material,  and  form- 
ing the  intermediate  electrodes.  The  liquid  enters  the  elec- 
trolyzer through  the  passage  d,  one  of  which  leads  into  each 
compartment.  As  soon  as  the  current  is  turned  on,  gas  is  pro- 
duced in  each  compartment,  which  rises  and,  carrying  the  liquid 
with  it,  causes  it  to  flow  through  the  channels  e,  as  shown  by 
the  arrows.  This  automatic  circulation  is  very  efficient.  A 
cooling  coil  in  the  container  prevents  the  temperature  from 
rising  too  high.  The  electrolysis  is  continued  till  the  concen- 
tration of  the  hypochlorite  has  reached  the  desired  value. 


Ibsss^^^^^ 


1" 


FIG.  38.  —  Vertical  section  of  Haas  and  Oettel  cell 

This  cell  was  never  put  on  the  market  in  this  country  in  the 
form  shown,4  but  an  improved  cell  is  made  by  the  National 
Laundry  Machinery  Company  of  Dayton,  Ohio,  the  details  of 
which  are  not  now  available. 

Among  a  number  of  other  factors,  the  cost  of  the  production 

8  U.  S.  Pat.  718,249,  (1903). 

4  Communication  from  the  National  Laundry  Machinery  Company. 


ELECTROLYSIS   OF   ALKALI   CHLORIDES 


121 


of  hypochlorite  depends  on  the  cost  of  salt  and  of  power,  and 
on  the  concentration  of  the  hypochlorite  produced ;  for,  as  was 
shown  above,  the  current  efficiency  of  the  production  of  hypo- 
chlorite approaches  zero  as  the  concentration  increases.  For 
cotton  bleaching  the  hypochlorite  is  diluted  to  three  grams  of 
active  chlorine  per  liter,  and  is  discarded  after  using.5  Less 
salt  will  therefore  be  lost  if  as  much  as  possible  is  changed  to 
hypochlorite,  but  the  cost  of  power  increases  as  the  concentra- 
tion increases.  The  concentration  to  which  it  will  be  most 
economical  to  continue  the  electrolysis  will  therefore  depend 
on  the  relative  cost  of  power  and  of  salt,  assuming  all  other 
conditions  of  the  experiment  constant.  There  will  then  be  a 
concentration  of  hypochlorite  for  which  the  cost  will  be  a  mini^ 
mum,  assuming  a  definite  cost  for  the  salt  and  the  power. 
This  minimum  cost  is  found  by  plotting  as  ordinates  the  cost 


TABLE  15 

The  Kellner  Cell 


ORIGINAL  NaCl 
CONC.  KG.  PER 
100  L. 

AMPERES  PER 
CELL 

GRM.  ACTIVE 

C12    PER    L. 

PER  CENT 
CURRENT 
YIELD 

KW.  HR.  PER 
KG.  ACTIVE 
Cl, 

KG.  SALT  PER 
KG.  ACTIVE 
01, 

6.3 

120 

1.84 

77.8 

5.9 

34.2 

6.3 

120 

3.34 

68.8 

6.7 

18.9 

6.3 

120 

7.06 

61.8 

7.4 

8.9 

6.3 

120 

10.01 

44.5 

10.3 

6.3 

10.0 

137 

3.09 

81.5 

5.2 

32.4 

10.0 

137 

6.85 

68.6 

6.2 

14.6 

10.0 

137 

10.44 

58.2 

7.3 

9.6 

10.0 

137 

12.96 

45.9 

9.2 

7.7 

15.0 

126 

3.00 

82.3 

5.1 

50.0 

15.0 

126 

6.28 

73.0 

5.7 

23.9 

15.0 

126 

10.50 

65.3 

6.4 

14.3 

15.0 

126 

13.50 

54.2 

7.7 

11.1 

20.0 

130 

2.48 

90.1 

4.5 

80.7 

20.0 

130 

6.58 

78.0 

5.2 

30.4 

20.0 

130 

10.09 

70.0 

5.8 

19.8 

6  W.  H.  Walker,  Trans.  Am.  Electrochem.  Soc.  9,  23,  (1906). 


122 


APPLIED   ELECTROCHEMISTRY 


of  power  for  a  definite  amount  of  hypochlorite  at  different  con- 
centrations, and  also  as  ordinates  the  cost  of  the  salt  required  for 
the  different  concentrations  of  hypochlorite.  The  curve  repre- 
senting the  sum  of  these  costs  will  be  found  to  have  a  minimum 
value. 

Table  15  gives  some  data  on  the  yield  of  active  chlorine  in 
the  Kellner  cell,  taken  from  cells  in  actual  operation.6 

The  yields  of  active  chlorine  in  the  Haas  and  Oettel  appara- 
tus are  given  in  Table  16  7 


TABLE  16 
The  Haas  and  Oettel  Cell 


GEM.  ACTIVE 

Clj  PER  L. 

PER  CENT  CURRENT  YIELD 

KW.  HR.  PER  KG. 
ACTIVE  C12 

KG.  SALT  PER  KG. 
ACTIVE  C12 

2.55 

95.0 

3.31 

66.6 

4.59 

82.4 

3.82 

37.0 

8.82 

64.8 

4.85 

19.3 

12.30 

56.7 

5.54 

13.8 

14.31 

52.8 

5.96 

11.9 

The  yields  in  active  chlorine  for  the  Schuckert  cell  are  given 
in  Table  17.1 


TABLE  17 

The  Schuckert  Cell 


ORIGINAL  NaCl 
CONC.  PER  CENT 

GRM.  ACTIVE  C12  PER  L. 

KW.  HR.  PER  KG. 
ACTIVE  C12 

KG.  SALT  PER  KG. 
ACTIVE  C12 

10 

10-22 

7 

5-  5.3 

10 

16 

6 

6-  6.5 

10 

10-12 

5 

10-10.6 

15 

20-22 

5.5-6 

7.5-  8 

15 

10-12 

4.5-5 

15-16 

6  Englehardt,  I.e.  p.  158. 

7  Oettel,  Z.  f.  Elektroch.  7,  315,  (1900). 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  123 

Chlorate  Cells.  —  Since  chlorate  is  made  directly  from  hypo- 
chlorite,  a  chlorate  cell  would  not  be  expected  to  differ  from  a 
hypochlorite  cell  in  any  mechanical  details.  The  earlier  chlo- 
rate cells,  however,  contained  a  diaphragm,  and  the  cathode 
solution  was  allowed  to  circulate  to  the  anode  compartment. 
This  was  to  prevent  the  reduction  of  the  hypochlorite  from 
which  the  chlorate  is  produced  ;  but  since  the  discovery  of  the 
action  of  potassium  chromate,  reduction  can  be  avoided  with- 
out a  diaphragm. 

The  first  process  to  be  used  in  practice  was  that  of  Gall  and 
Montlaur,  patented  in  1884. 8  This  cell  originally  contained  a 
diaphragm  to  prevent  reduction,  and  the  solution  circulated 
from  the  cathode  to  the  anode  by  means  of  external  pipes.  The 
solution  must,  of  course,  leave  the  anode  compartment  as  rapidly 
as  it  flows  in,  but  whether  it  leaves  the  cell  entirely  or  returns 
to  the  cathode  compartment  is  not  stated.  Since  1897  the 
diaphragms  have  been  given  up.  A  plant  employing  this  pro- 
cess was  put  in  operation  at  Vallorbe  in  1891,  and  another  in 
St.  Michel,  Savoy,  in  1896.  Very  little  information  concerning 
these  plants  has  been  published. 

In  1892  the  National  Electrolytic  Company  at  Niagara  Falls 
employed  the  chlorate  cell  of  W.  T.  Gibbs.9  A  number  of 
these  cells  clamped  together  are  shown  in  Figure  39,  and  a  side 
elevation  of  one  cell  on  the  line  22  of  the  preceding  figure,  in 
Figure  40. 10  Each  cell  consists  of  a  frame  A  made  of  wood  with 
a  metallic  resistant  lining  B.  The  rods  0  forming  the  cathode 
are  attached  on  one  side  of  this  frame,  and  on  the  other,  the 
anode,  consisting  of  a  metallic  plate  D  faced  with  platinum  E. 
Copper  is  preferred  for  the  cathode  and  lead  for  the  plate  D. 
Successive  frames  are  separated  from  each  other  by  gaskets  F. 
G-  are  supply  tubes  and  .ff  are  vents  for  the  escape  of  gas  and 
liquid.  The  cells  are  clamped  together  by  the  plates  JK  and 
the  bolts  L.  Each  pair  of  electrodes  is  separated  by  the  corre- 
sponding gasket.  The  horizontal  insulating  rods  0  prevent 

8  J.  B.  C.  Kershaw,  Die  Elektrolytische  Chloratindustrie,  p.  19,  (1905). 

9  J.  W.  Richards,  Electrochern.  Ind.  1,  19,  (1902). 
10  TJ.  S.  Pat.  665,426,  (1901). 


124 


APPLIED    ELECTROCHEMISTRY 


short  circuit  between  the  anodes  and  cathodes,  which  are  only 
from  1  to  3  millimeters  apart.  The  electrolyte  circulates  from 
the  cell  to  a  cooling  vessel  where  the  chlorate  is  precipitated. 


FIG.  39.  —  Gibb's  cells  clamped  together 

More  chloride  is  then  added,  and  the  solution  is  returned  to  the 
electrolyzing  cell.  A  convenient  size  for  these  cells  is  65  by 
4-3  centimeters  and  7.5  centimeters  thick. 


ELECTROLYSIS    OF   ALKALI   CHLORIDES 


125 


The  cell  of  Lederlin  and  Corbin,  used  at  Chedde,  is  of  the 
open  type.11  It  contains  a  platinum  anode  and  two  cathodes  of 
copper,  bronze,  brass,  or  iron.  The  anode  has  an  area  of  10 
square  centimeters  and  the  cathode,  32. 


FIG.  40.  —  Section  of  single  Gibb's  cell 


The  chlorate  is  generally  purified  by  recrystallization,  and 
the  recrystallizing  apparatus  is  an  important  part  of  a  chlorate 
plant. 

The  yield  at  Vallorbe  was  at  first  55.9  grams  per  kilowatt 
hour,  though  this  has  since  been  considerably  increased.12 


11  Kershaw,  I.e.  p.  38. 


Kershaw,  I.e.  p. 


126 


APPLIED   ELECTROCHEMISTRY 


The  yield  obtained  at  Chedde  with  the  Lederlin  and  Corbin 
cell  in  a  slightly  acid  solution  containing  potassium  bichromate 
was  0.69  gram  per  ampere  hour,  or  90  per  cent  of  the  theoretical. 

Perchlorates.  —  The  cells  used  for  the  production  of  chlorates 
can  be  used  equally  well  for  perchlorates.  Whether  there  is  a 
difference  in  practice  cannot  be  stated,  for  no  description  of  a 
perchlorate  cell  has  been  published. 

Alkali  Hydrates  and  Chlorine.  —  In  cells  in  which  hydrate 
and  chlorine  are  to  be  the  final  product,  the  anode  must  be  sep- 
arated from  the  cathode  so  that  the  chlorine  and  hydrate  can- 
not mix.  In  the  first  type  of  cell  to  be  considered,  this  is 
accomplished  by  means  of  a  porous  diaphragm.  A  very  large 
number  of  such  cells  have  been  patented,  but  only  a  few  need 
be  described. 

One  of  the  simplest  of  the  diaphragm  cells  is  McDonald's, 
used  by  the  Clarion  Paper  Mill  at  Johnsonburg,  Pennsylvania,13 
and  the  United  States  Reduction  and  Refining  Company  in 
Colorado.  At  the  latter  plant,  there  are  75  cells,  producing 
1500  pounds  of  chlorine  in  24  hours.14  Two  vertical  sections  of 


LENGTHS  SECTION. 


CROSS  SECTION. 


BBBBSBBBB 


FIG.  41.  — McDonald  cell 

the  cell  are  shown  in  Figure  41.  It  consists  of  a  cast-iron  tank, 
1  foot  wide,  1  foot  high,  and  5  feet  and  2  inches  long,  with 
two  longitudinal  perforated  partitions.  The  perforations  are 
•£%  inch  in  diameter,  and  there  are  4  or  5  to  the  square  inch. 
A  diaphragm  is  placed  next  each  partition  in  the  middle  com- 

13  Electrochem.  Ind.  1,  387,  (1903). 

14  J.  B.  procker,  Electrochem.  and  Met.  Ind.  5,  201,  (1907). 


ELECTROLYSIS    OF   ALKALI   CHLORIDES  127 

partment,  containing  the  anode.  The  diaphragms  consist  of 
asbestos  paper  fastened  to  asbestos  cloth  by  sodium  silicate,  and 
are  held  in  position  by  cement  placed  over  both  end  walls  and 
the  bottom  of  the  anode  compartment.  This  compartment  is 
closed  by  a  cast-iron  cover  5  inches  deep,  6  inches  wide,  and 
nearly  5  feet  long,  into  which  the  anodes  are  cemented.  It  is 
lined  with  cement  and  painted  inside  with  asbestos  varnish. 

The  anode  cohsists  of  blocks  of  graphitized  carbon,  4  inches 
square  and  10  inches  long,  into  each  of  which  a  copper  rod  is 
fastened  by  lead  for  the  electrical  connection.  The  partition 
walls  form  the  cathode. 

The  partition  walls  are  flanged,  forming  a  seat  to  hold  the 
cover,  which  is  surrounded  by  a  layer  of  cement.  The  chlorine 
is  conducted  from  the  anode  compartment  by  a  lead  pipe  to  a 
gas  main  which  leads  to  absorbing  towers  containing  lime- 
water.  Brine  circulates  through  the  anode  compartment. 

The  diaphragms  last  about  8  months,16  after  which  time  the 
pores  become  clogged. 

The  sodium  hydrate  solution  leaving  the  cathode  compart- 
ment contains  from  7  to  18  per  cent  sodium  hydrate.  When 
the  diaphragm  is  new,  the  level  of  the  liquid  in  the  anode  arid 
cathode  compartments  is  nearly  the  same,  but  when  it  becomes 
more  or  less  stopped  up,  the  depth  of  the  liquid  -in  the  cathode 
compartment  is  only  an  inch  or  two. 

The  Hargreaves-Bird  cell  consists  of  a  cast-iron  box  10  feet 
in  length,  14  inches  in  width,  and  5  feet  in  height.16  It  is 
divided  into  three  compartments  by  two  diaphragms  made  on 
heavy  copper  gauze,  which  forms  the  cathode.  The  space 
between  the  diaphragms  is  the  anode  compartment,  through 
which  brine  circulates.  There  is  no  liquid  in  the  anode  com- 
partment except  what  percolates  through  the  diaphragm. 
Steam  and  carbonic  gas  are  blown  through  the  two  outer  com- 
partments and  change  the  hyrate  formed  on  the  outside  of  the 
diaphragm  to  sodium  carbonate.  This  cell  takes  2000  amperes 
at  from  4  to  4.5  volts.  The  anode  is  a  row  of  gas  carbons, 

is  L.  Rostosky,  Z.  f.  Elektroch.  11,  21,  (1905). 
is  Electrochero.  and  Met.  Ind.  3,  350,  (1905). 


128 


APPLIED   ELECTROCHEMISTRY 


which  last  30  to  40  days.     The  diaphragms  last  about  the  same 
length  of  time. 

The  Hargreaves-Bird  cell  is  shown  in  Figure  42,  which  is  a 
partial  longitudinal  section  and  side  elevation,  and  in  Figure 
43,  which  is  a  section  perpendicular  to  the  length.17  The 
outside  frame  I  is  of  iron  lined  with  cement  and  bricks  w, 
which  are  saturated  with  tar  to  prevent  leakage.-  The  space 


FIG.  42.  —  Hargreaves-Bird  cell,  side  elevation 

/  is  the  anode  compartment  through  which  the  chloride  solution 
circulates,  entering  through  the  pipe  g  and  leaving  through  h. 
The  diaphragms  are  made  of  asbestos  paper,  the  pores  of  which 
have  been  filled  with  hydrated  silicate  of  lime  or  magnesia.18 
In  the  cathode  chamber  a  number  of  copper  strips  b  are  placed, 
imbedded  in  cement  e,  extending  from  the  cover  plate  c  to  the 
cathode  c?,  and  inclined  downwards.  These  direct  the 


17  U.  S.  Pat.  655,343,  (1900). 


U.  S.  Pat.  596,157,  (1897). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES 


129 


densed  vapor  against  the  cathode  to  wash  away  the  alkali  as  it 

is  formed.     The  lower  edges  of  the  strips  have  openings,  in 

order  to  allow  the  steam  and  gas  to 

pass  freely  over  the  cathode,    a',  ar  are 

the   injectors   for   supplying   carbonic 

acid   gas   and   steam   to    the    cathode 

chambers.     Z2,  Z2  are  pipes  for  draining 

the  cathode  chambers.      The  chlorine 

passes  from  the  anode  chambers  to  the 

towers,  where  it  is  absorbed  by  milk 

of  lime. 

The  West  Virginia  Pulp  and  Paper 

Company,  Me- 

chaiiicsville, 

New  York,  use 

this  cell   for 

making      their 

bleaching  solu- 
tions.19    This 

plant     consists 

of  two  rows  of 

14    cells    each, 

n 


LJ\ 


FIG.  43.  —  Harsreaves-Bird  cell, 
end  section 


all  connected  in  series. 

Perhaps  the  most  efficient  diaphragm 
cell  in  use  is  the  Townsend  cell,  repre- 
sented in  cross  section  in  Figure  44, 
and  in  perspective  in  Figure  45.20  The 
anode  space  is  inclosed  between  a  lid  (7, 
two  vertical  diaphragms  D,  and  a  non- 
conducting body  H.  Graphite  anodes 
pass  through  the  lid  on  the  cell.  The 
perforated  iron  cathode  plates  S  are  in 
close  contact  with  the  diaphragms.  These  plates  are  fastened 
to  two  iron  sides  J,  which  form  the  cathode  compartment.  The 
anode  compartment  is  filled  with  brine  T,  and  the  cathode  corn- 

is  Electrochem.  and  Met.  Ind.  6,  227,  (1908). 
20  Electrochem.  and  Met.  Ind.  5,  209,  (1907). 


FIG.  44.  —  Townsend  cell 


130 


APPLIED   ELECTROCHEMISTRY 


partment  with  kerosene  oil  K.  The  brine  percolates  through 
the  diaphragm,  and,  when  the  current  is  turned  on,  it  contains 

hydrate.  The 
aqueous  solution, 
on  passing  the  dia- 
phragm, comes  in 
contact  with  the 
kerosene  and 
forms  drops  which 
fall  to  the  bottom 
of  the  compart- 
ment, are  collected 
in  the  pocket  A, 
and  are  drained  off 
through  P.  The 
solution  leaving  P 
contains  150  grams 
of  sodium  hydrate 
and  213  grams  of 
salt  per  liter.  The 
salt  is  separated 
by  evaporation  and 
is  used  over  again. 

The  continual  percolation  prevents  nearly  all  diffusion  of  hy- 
drate back  to  the  anode.  The  rate  of  percolation  for  a  2500- 
ampere  cell  is  from  15  to  30  liters  an  hour.21 

The  Town  send  cell  is  8  feet  in  length,  3  feet  in  depth,  and 
1  foot  in  width,  and  consists  of  a  U-shaped  concrete  body 
against  which  the  two  iron  side  plates  are  clamped.  A  rubber 
gasket  is  placed  between  the  concrete  and  the  iron  to  make  a 
tight  joint.  Brine  circulates  through  the  anode  compartment, 
and  during  its  passage  the  specific  gravity  falls  from  1.2  to 
1.18.  On  leaving  the  cell  it  is  resaturated  and  is  then  ready  to 
be  passed  through  again.  There  is  a  loss  in  kerosene  which 
amounts  in  cost  to  about  two  dollars  a  day  for  a  large  plant. 
The  diaphragms  of  the  Townsend  cell  consist  of  a  woven 

21  Baekeland,  Electrochem.  and  Met.  Ind.  7,  314,  (1909). 


FIG.  45.  —  Townsend  cell 


ELECTROLYSIS  OF  ALKALI  CHLORIDES 


131 


sheet  of  asbestos  cloth,  the  pores  of  which  are  filled  with  a  mix- 
ture of  iron  oxide,  asbestos  fiber,  and  colloid  iron  hydroxide. 
This  mixture  is  applied  with  a  brush  like  ordinary  paint.  Di- 
aphragms may  be  renovated  by  scrubbing  and  washing  the 
surface  with  water,  allowing  to  dry,  and  repainting  with  this 
mixture.  This  operation  is  not. necessary  more  than  once  in 
five  weeks,  and  sometimes  not  for  several  months. 

The  current  efficiency  of  the  Townsend  cell  is  as  high  as  96 
or  97  per  cent  under  ordinary  conditions,  with  a  current  density 
on  the  anode  of  1  ampere  per  square  inch  and  about  4  volts  on 
each  cell.22  This  cell  has  been  in  use  at  Niagara  Falls  in  the 
plant  of  the  Development  and  Funding  Company  since  1906. 
This  plant  originally  consumed  1000  kilowatts,  and  according 
to  latest  accounts  it  was  being  increased  to  four  times  this 
capacity.21 

Not  much  information  concerning  the  bell  process  as  actually 
arranged  in  practice  is  available.  The  process  is  carried  out  by 
the  Oesterreiche 
Verein  fur 
Chemische  und 
Metallurgische 
Production  in 
Aussig,  and  at 
several  places  in 
Germany.  Fig- 
ure 46  shows 


FIG.  46.  —  Cell  for  Bell  process 


two  cross  sections  of  the  cell,  25  of  which  are  placed  side  by 
side  in  each  bath.23  The  solution  leaving  the  bath  is  said  to 
contain  100  to  150  grams  of  alkali  hydrate  per  liter,  at  a  cur- 
rent yield  of  85  to  90  per  cent  and  with  4  to  4.5  volts  per  cell.24 
The  Castner  cell25  is  represented  in  Figure  30.  It  is  a  slate 
box  4  feet  square,  and  6  inches  deep,  the  joints  of  which  are 

22  For  laboratory  tests  on  the  efficiency  of  this  cell,  see  Richardson  and  Patter- 
son, Trans.  Am.  Electrochem.  Soc.  7,311,  (1910). 
28  Z.  f.  Elektroch.  7,  925,  (1901). 
24  Haeussermann,  Dinglers  polyt.  J.  315,  475,  (1900). 
25 U.S.  Pat.  528,322,  (1894). 


132 


APPLIED   ELECTROCHEMISTRY 


made  tight  with  rubber  cement.26  Two  partitions,  reaching  to 
within  ^g  inch  of  the  bottom,  divide  the  cell  into  three  compart- 
ments. The  two  outside  compartments  contain  the  graphite 
anodes  A,  and  the  middle  compartment,  the  iron  cathode  0. 
Brine  circulates  through  the  anode  compartments,  and  pure 
water  is  supplied  to  the  cathode  compartment.  The  cell  is  piv- 
oted on  two  points  at  one  end  and  the  other  is  raised  and  lowered 


FIG.  47.  —  Whiting  electrolytic  cell,  plan 

about  J  inch  once  a  minute,  causing  the  mercury  to  circulate  be- 
tween the  anode  and  cathode  compartments.  The  hydrate 
leaving  the  cathode  compartment  has  a  specific  gravity  of  1.27. 
This  is  evaporated  to  solid  hydrate  in  large  iron  pans.  Each 
cell  takes  about  100  pounds  of  mercury,  which  is  a  very  large 
item  of  expense.  The  current  for  each  cell  is  630  amperes  at 
4.3  volts,  and  the  current  efficiency  is  about  90  per  cent. 

ae  J.  W.  Richards,  Electrochem.  Ind.  1,  12,  (1902). 


ELECTROLYSIS    OF   ALKALI    CHLORIDES  133 

The  Whiting  mercury  cell  is27  of  a  different  type  from  the 
Castner  cell.  The  sodium  is  not  electrolyzed  out  of  the  amal- 
gam, but  the  amalgam  is  withdrawn  from  the  electrolyzing 
chamber  and  treated  with  water  in  a  decomposing  chamber 
where  the  hydrate  is  formed.  A  number  of  electrolytic  com- 
partments are  placed  in  parallel  and  are  operated  successively. 


B 


"b 


FIG.  48.  —  Whiting  electrolytic  cell,  cross  section 

so  that  the  cell  is  continuous  in  its  action,  though  intermittent 
in  principle. 

This  cell,  shown  in  Figures  47,  48,  and  49,  is  a  massive  con- 
crete structure  supported  on  four  concrete  pedestals,  from 
which  it  is  insulated.  It  consists  of  a  shallow  box  divided  into 
two  compartments,  A  and  B,  by  a  concrete  partition.  The 
bottom  of  the  decomposing  chamber  is  divided  by  low  glass 
partitions  into  a  number  of  sections  having  V-shaped  bottoms 

^  Jasper  Whiting,  Trans.  Am.  Electrochem.  Soc.  17,  327,  (1910). 


134 


APPLIED    ELECTROCHEMISTRY 


sloping  at  a  slight  angle  towards  the  central  slot  D.  These 
slots  lead  through  the  concrete  partition  into  the  oxidizing 
chamber  B,  where  they  turn  upward  and  are  closed  by  valves 
E.  The  valves  are  operated  by  the  cams  F,  which  are  attached 
to  a  slowly  revolving  shaft  Gr.  The  other  ends  of  the  slots  are 
connected  by  the  channel  H,  called  the  distributing  level. 
This  connects  with  a  secondary  channel  /,  which  leads  through 
one  of  the  side  walls  of  the  cell  to  a  pump  J",  at  the  extreme 
end  of  the  oxidizing  compartment.  Mercury  covers  the  bottom 
of  the  decomposing  compartment,  filling  the  above-described 
sections  to  a  common  level.  The  anodes  K  are  slabs  of 
Acheson  graphite,  perforated  to  allow  the  chlorine  to  escape, 
and  rest  upon  the  ledges  L,  placed  at  the  ends  of  the  section  in 


FIG.  40.  —  Whiting  electrolytic  cell,  longitudinal  section 

such  a  way  as  to  make  a  very  short  distance  between  the  anode 
and  the  mercury  cathode.  The  anodes  are  connected  to  the 
dynamo  by  the  leads  M. 

The  oxidizing  chamber  is  divided  into  three  compartments 
P,  lined  with  graphite  and  sloping  downward  in  successively 
opposite  directions,  forming  a  zigzag  path  to  the  pump  pit  Q, 
where  the  stoneware  rotary  pump  J  is  placed.  Brine  fills  the 


ELECTROLYSIS    OF    ALKALI    CHLORIDES  135 

decomposing  chamber,  and  water  or  alkali  hydrate  fills  the  oxi- 
dizing chamber. 

The  action  is  as  follows  :  The  floor  of  several  sections  of  the 
decomposing  chamber  is  covered  with  mercury,  maintained  at 
a  common  level  by  the  distributing  level.  The  current  flows 
from  the  anode  through  the  brine  to  the  mercury  and  out  by 
the  iron  rods  R,  partly  imbedded  in  the  concrete.  When  the 
electrolysis  has  proceeded  about  two  minutes,  the  valve  at  the 
point  of  exit  of  one  of  the  sections  is  opened  by  the  action  of 
the  cam,  and  the  entire  mass  of  sodium  amalgam  in  the  section 
sinks  into  the  slot  and  through  the  connecting  pipe  into  the 
oxidizing  chamber.  When  the  mercury  is  out  of  the  cell,  the 
valve  is  closed  by  the  cam.  Mercury  free  from  sodium  then 
flows  into  the  empty  chamber  by  way  of  the  distributing  level, 
until  the  common  level  is  reached.  In  the  meantime  the 
sodium  amalgam  in  the  oxidizing  chamber  flows  by  gravity 
over  the  graphite  plates  P  to  the  pump  pit.  On  reaching  this 
point  the  mercury  has  been  deprived  of  its  sodium,  and  is 
raised  by  the  pump  into  the  wall  pipe  of  the  decomposing 
chamber,  completing  the  cycle. 

The  brine  is  fed  in  between  the  electrodes  from  the  recep- 
tacles S,  equal  in  number  to  the  sections  of  the  decomposing 
chamber.  They  are  formed  in  the  cover  of  the  decomposing 
compartment,  and  are  connected  by  a  channel  T.  Glass  tubes 
lead  from  the  bottom  of  the  receptacle  S  through  the  anode 
and  terminate  below  the  surface  of  the  mercury  near  the  middle 
of  each  section.  As  long  as  the  sections  are  filled  with  mer- 
cury the  lower  ends  of  the  tubes  are  sealed,  but  when  the 
mercury  is  drawn  off,  a  definite  quantity  of  concentrated  brine 
flows  into  the  section. 

The  graphite  slabs  in  the  oxidizing  chamber  contain  a  large 
number  of  channels  through  which  the  mercury  flows.  The 
sides  of  the  channels  extend  into  the  caustic  solution  and  form 
the  cathode  of  a  short-circuited  couple.  It  is  difficult  to  main- 
tain good  contact  between  the  graphite  and  mercury  on  account 
of  the  hydrogen  evolved,  but  this  difficulty  was  overcome  by 
boring  holes  j-  inch  deep  and  J  inch  in  diameter  at  frequent 


136  APPLIED    ELECTROCHEMISTRY 

intervals  in  the  channels,  and  filling  them  with  pure  mercury 
at  the  start.  This  mercury  remains  pure  and  makes  good  con- 
tact with  the  amalgam  and  the  graphite. 

The  cell  used  at  the  Oxford  Paper  Company's  works  in  Rum- 
ford,  Maine,  is  1.8  meter  square.  It  consists  of  five  sections 
and  takes  a  current  of  from  1200  to  1400  amperes  at  4  volts. 
This  corresponds  to  an  anode  current  density  of  11  amperes 
per  square  decimeter.  The  current  efficiency  is  from  90  to  95 
per  cent.  The  temperature  is  about  40  degrees.  Each  cell 
requires  from  350  to  375  pounds  of  mercury.  A  20  per  cent 
hydrate  solution  is  obtained,  though  one  with  49  per  cent  can 
be  made  if  desired.  The  chlorine  gas  is  98  per  cent  pure,  the 
remaining  2  per  cent  being  hydrogen. 


CHAPTER  VII 


THE   ELECTROLYSIS   OF   WATER 

HYDROGEN  and  oxygen  have  a  number  of  technical  applica- 
tions that  require  their  manufacture  on  a  large  scale.  Such 
uses  are  welding  with  the 
oxyhydrogen  flame,  as  is  done 
in  joining  the  lead  plates  of 
storage  batteries;  hydrogen 
is  used  for  filling  balloons, 
and  oxygen  is  used  for  chem- 
ical and  medicinal  purposes. 

Hydrogen  and  oxygen  are 
produced  on  a  commercial 
scale  by  the  electrolysis  of 
aqueous  solutions,  and  of 
course  the  object  of  the  large 
number  of  patents  taken  out 
in  this  field  is  to  keep  the 
hydrogen  and  oxygen  separate 
from  each  other.  For  this 
purpose  the  anode  and  cathode 
compartments  have  to  be  sep- 
arated by  a  partition  of  some 
kind.  The  different  methods 
of  separating  the  gases  will  be 


Schnitt 


FIGS.  50-53.  —  Schmidt's  apparatus  for  the 
electrolysis  of  water 


illustrated  in  the  description 
of  the  following  cells. 

The  cell  designed  by  Dr.  O.  Schmidt1  is  shown  in  sections 
in  Figures  50-53,  and  a  general  view  in  Figure  54.     It  consists 

1  Engelhardt,  Die  Elektrolyse  des  Wassers,  p.  24,  (1902);  Z.  f.  Elektroch.  7, 
294,  (1901). 

137 


138 


APPLIED   ELECTROCHEMISTRY 


of  a  number  of  iron  plates  e  having  thick  rims  and  separated 
by  diaphragms  d.  These  plates  are  the  cathode  in  one  cell  and 
the  anode  of  the  following  cell.  Each  plate  has  two  holes  in 
the  thick  rims  h,o  and  w,  w' ,  so  that  the  apparatus  is  traversed 
above  and  below  by  two  canals.  The  lower  canals  are  for  sup- 
plying the  water  as  it  is  decomposed,  and  the  upper  are  for  al- 


FIG.  54.  —  Schmidt's  apparatus  for  the  electrolysis  of  water 

lowing  the  gases  to  escape.  The  canals  w  and  h  connect  with 
the  cathode  chambers,  w'  and  o  with  the  anode  chambers.  The 
two  canals  for  adding  water,  w  and  w',  are  connected  with  a 
common  filling  tube  W  by  the  pipes  w2,  up,  and  at  the  other  end 
of  the  apparatus  the  two  gas  canals  connect  with  reservoirs  .ZTand 
0,  where  the  gas  is  separated  from  the  liquid  carried  along  with 
it.  The  liquid  then  returns  to  its  respective  chamber  in  the 
electrolyzer.  The  stopcock  a  is  for  emptying  the  apparatus. 

The  diaphragms  are  of  asbestos  with  rubber  edges  to  prevent 
leakage.  The  electrolyte  is  a  dilute  solution  of  potassium  car- 
bonate. Each  cell  has  2.5  volts  impressed,  and  the  current 
yield  is  nearly  100  per  cent.  The  oxygen  is  on  the  average 


THE    ELECTROLYSIS   OF   WATER 


139 


97  per  cent  pure,  while  the  hydrogen  is  99  per  cent.     Either 
gas  may  be  purified  by  passing  through  red-hot  porcelain  tubes. 


TS* 


FIG.  55.  —  Garuti  and  Pompili's  electrolyzer 

which  combines  the  small  impurity  of  hydrogen  in  the  oxygen, 
or  of  oxygen  in  the  hydrogen,  to  water  which  is  easily  removed. 


FIG.  56.  — Garuti  and  Pompili's  electrolyzer 

This  apparatus  is  made  at  the  Maschinenfabrik  Oerlikon. 
near  Zurich,  Switzerland. 


140 


APPLIED   ELECTROCHEMISTRY 


An  apparatus  in  which  the  separation  of  the  hydrogen  and 
oxygen  is  effected  by  a  different  method  is  that  of  Garuti  and 
Pompili.2  In  this  cell  a  partition  of  iron  separates  the  anode 
from  the  cathode,  and  this  partition  is  prevented  from  becom- 
ing an  intermediate  electrode 
by  keeping  the  voltage  ap- 
plied to  the  cell  too  low  for 
this  to  take  place.  The  cur- 
rent flows  from  the  anode  to 
the  cathode  around  the  bot- 
tom of  the  iron  partition. 

Figure  55  is  a  longitudinal 
vertical  section  through  the 
center,  Figure  56  is  a  horizon- 
tal section  of  one  end,  Figure 

57  is  a  vertical  cross  section 
of  the  apparatus,  and  Figure 

58  a  plan  view  of  conductor 
and  electrodes. 

A  tank  A  of  wood  lined  with 
iron  a  contains  the  electro- 
lyzer,  which  consists  of  an 
inverted  tank  A1  which  is  di- 
vided into  cells  E  by  longitu- 
dinal diaphragms.  This  cell 
is  made  of  iron  and  is  open 

4^  £^         only    at    the    bottom.       The 

l^\  I     \         anodes   b  and  cathodes  c  are 

placed  one  in  each  cell,  taking 
care   that  each   anode  is  be- 


FIG.  57.  —  Garuti  and  Poinpili's  electro- 
lyzer 


tween  two  cathodes.  The  gas  passes  through  an  opening  at 
the  top  of  each  chamber  into  the  reservoir  containing  the  same 
gas.  The  electrodes  are  insulated  from  the  diaphragms  by 
combs  I  made  of  wood,  the  teeth  of  which  enter  the  cells  and 
fill  the  spaces  between  the  electrodes  and  diaphragm.  L  is  a 
handle  for  lifting  out  the  electrolyzer. 

2U.  S.  Patent  629,070,  (1899). 


THE    ELECTROLYSIS    OF   WATER 


141 


A  25  per  cent  solution  of  potassium  hydrate  is  used.  The 
voltage  per  cell  is  not  allowed  to  exceed  3  volts,  so  there  is  no 
danger  of  the  diaphragm  acting  as  an 
electrode.  The  diaphragms  may  be  per- 
forated near  the  bottom  with  a  large  num- 
ber of  small  holes,  as  there  is  very  little 
danger  of  the  gases  becoming  mixed  at 
this  point. 

The  hydrogen  obtained  from  this  ap- 
paratus is  98.9  per  cent  pure,  the  oxygen 
97.  This  apparatus  is  used  in  Rome, 
Tivoli,  Brussels,  and  Lucern. 

The  cell  of  the  Siemens  Brothers  and 
Company  and  Obach  3  employs  a  parti- 
tion which  consists  of  metal  gauze  below 
the  water  line.  The  current  is  con- 
ducted through  the  meshes,  which  are 
small  enough  to  prevent  the  mixture  of  the  gases. 

Other  cells,  such   as  that  of  Schoop,4   have   nonconducting 
partitions. 

These  examples  complete  the  different  principles  on  which 
technical  cells  for  the  decomposition  of  water  are  built. 


FIG.  58.  —  Garuti  and  Pom- 
pili's  electrolyzer 


3  Engelhardt,  I.e.  p.  67. 


4  Engelhardt,  I.e.  p.  44. 


CHAPTER   VIII 

PRIMARY   CELLS 

A  PRIMARY  battery  is  a  cell  so  arranged  that  the  energy  of 
a  chemical  reaction  is  obtained  as  an  electric  current,  and  in 
which  the  chemicals  are  not  regenerated  by  passing  the  current 
through  the  cell  in  the  opposite  direction.  When  the  battery 
is  run  down,  fresh  chemicals  must  be  supplied.  A  secondary 
battery,  or  accumulator,  is  a  battery  in  which  chemicals  are 
regenerated  by  passing  through  the  cell,  after  discharge,  a 
reverse  current  from  some  other  source. 

Before  the  invention  of  dynamos,  primary  batteries  were  the 
main  source  of  electric  energy;  but  since  this  method  of  gener- 
ating electricity  is  too  expensive  for  use  where  a  large  quan- 
tity of  energy  is  needed,  they  were  employed  only  for  very 
light  work  and  for  experimental  purposes.  They  are  still  used 
extensively  for  electric  bells,  for  exploding  the  gases  in  engines 
by  electric  sparks,  railroad  signals,  and  similar  purposes. 
Primary  batteries  of  special  forms  are  also  the  standards  of 
electromotive  force,  but  this  is  rather  a  purely  scientific  branch 
of  the  subject  than  a  technical  application,  and  will  therefore 
be  omitted. 

The  first  primary  battery  was  due  to  Volta,  and  consisted  in 
a  negative  pole  of  zinc  and  a  positive  pole  of  copper  dipping 
into  a  solution  of  salt  or  dilute  acid.  The  electromotive  force 
of  this  battery  rapidly  falls  off  if  an  appreciable  current  is 
taken  from  it,  on  account  of  the  hydrogen  liberated  on  the 
positive  pole.  This  develops  a  back  electromotive  force  and 
also  increases  the  resistance  of  the  cell  itself.  The  battery  is 
then  said  to  be  polarized.  In  order  to  have  a  battery  that  is  at 

142 


PRIMARY    CELLS  143 

all  efficient,  polarization  must  be  avoided.  In  the  Smee  cell, 
this  was  done  by  substituting  platinized  silver  for  the  positive 
pole  in  place  of  the  copper  in  the  Volta  cell.  The  rough  sur- 
face caused  the  bubbles  of  hydrogen  to  escape  more  rapidly. 
In  the  Grove  battery,  devised  in  1831,1  the  cathode  consisted 
of  platinum  dipping  into  nitric  acid  contained  in  a  porous  cup. 
Outside  the  cup  was  dilute  sulphuric  acid  and  a  zinc  negative 
pole.  In  this  case  the  nitric  acid  acts  as  a  depolarizer,  oxidiz- 
ing the  hydrogen  to  water  and  itself  being  reduced  to  nitrous 
gases.  The  electromotive  force  of  this  battery  is  between  1.6 
and  1.7  volts. 

The  Bunsen  cell  is  a  Grove  cell  with  carbon  in  place  of  plat- 
inum for  the  positive  pole. 

In  the  chromic  acid  battery,  due  to  Poggendorff,  the  electrolyte 
is  a  solution  of  sulphuric  acid  and  potassium  bichromate.  The 
positive  pole  is  carbon  and  the  negative  zinc,  which  is  withdrawn 
from  the  battery  when  not  in  use.  The  chromic  acid  acts  as 
depolarizer.  The  electromotive  force  is  about  1.3  volts. 

These  batteries  have  at  present  little  more  than  historical  inter- 
est. The  use  of  primary  cells  is  now  nearly  entirely  confined 
to  the  Leclanche,  the  Lalande,  and  the  Daniell  cells.  Leclanche 
brought  out  his  cell  in  1868.2  It  consists  of  a  zinc  rod  forming 
the  negative  pole  and  dipping  into  a  solution  of  ammonium  chlo- 
ride. The  positive  pole  is  carbon  in  contact  with  manganese 
dioxide  for  a  depolarizer.  When  the  circuit  is  closed,  zinc  goes 
in  solution  as  zinc  chloride  and  the  ammonium  radical  is  deposited 
on  the  carbon,  which  breaks  up  into  ammonia  and  hydrogen. 
The  ammonia  dissolves  and  the  hydrogen  is  oxidized  by  the 
manganese  dioxide  to  water.  This  depolarization  is  not  rapid, 
however,  consequently  not  much  current  can  be  taken  from  a 
Leclanche  cell  at  a  time  without  the  voltage  dropping  consider- 
ably, but  it  recovers  on  standing.  The  electromotive  force  of 
this  cell  on  open  circuit  differs  from  one  cell  to  another,  varying 
from  1.05  to  1.8  volts. 

This  cell  is  put  on  the  market  under  a  large  number  of  different 

1  Wiedemann,  Die  Lehre  von  der  Elektricitat,  1,  867,  (1893). 

2  Wiedemann,  I.e.  p.  850. 


144 


APPLIED    ELECTROCHEMISTRY 


FIG.  59.  —  Carbon 
of  Sampson  cell 


forms  and  under  different  names.  One  of  the  best  Leclanche 
cells  on  the  market  is  the  Sampson  cell.3  The  carbon  of  this  cell 
is  shown  upside  down  in  Figure  59.  It  consists 
of  a  fluted  hollow  cylinder  of  French  carbon  pro- 
vided with  a  removable  seal  at  the  lower  end  and 
filled  with  a  mixture  of  carbon  and  manganese 
dioxide.  The  cell  set  up  is  shown  in  Figure  60. 
The  Lalande  cell,  brought  out  in  1883,4  con- 
sists of  zinc  for  the  negative  pole,  a  30  per  cent 
solution  of  potassium  hydrate  for  the  electro- 
lyte, and  a  plate  or  box  of  iron  or  copper  in 
contact  with  black  copper  oxide  as  depolarizer. 
The  hydrate  is  protected  from  the  carbonic  acid 
of  the  air  by  a  layer  of  oil.  The  zinc  goes  in 
solution  as  sodium  zincate,  and  the  hydrogen 
deposited  on  the  positive  plate  is  oxidized  by 
the  copper  oxide.  The  positive  plate  may  also  be  an  agglom- 
erate porous  plate  of  copper  oxide.  The  electromotive  force 
of  this  cell  is  about  0.9  volt  and  is  very  constant.  The  oxide 
when  reduced  to  copper  is  easily 
oxidized  again  by  heating  in  the 
air.  The  original  method  of  La- 
lande of  making  the  porous  copper 
oxide  plates  was  to  press  a  moist 
mixture  of  oxide,  4  or  5  per  cent 
clay,  and  6  to  8  per  cent  tar,  and 
then  to  heat  to  redness.  The 
plates  so  produced  were  porous 
and  lasted  well.  This  plate  must 
be  reduced  to  copper  over  its  en- 
tire surface  before  its  normal  rate 
is  reached,  on  account  of  the  poor 
conductivity  of  copper  oxide.  This  is  done  before  assembling 
the  plates. 

A  modern  type  of  the  Lalande  battery  is  made  by  the  Edison 

8  N.  H.  Sneider,  Modern  Primary  Batteries,  p.  10,  (1905). 
4  Wiedemann,  I.e.  p.  854. 


FIG.  00.  — The  Samson  cell 


PRIMARY   CELLS  145 

Manufacturing  Company  at  Orange,  New  Jersey,  and  is  called 
the  Edison-Lalande  Battery.  This  battery,  shown  in  Figure 
61,  consists  of  a  copper  oxide  plate  between  two  zinc  plates 
dipping  in  a  20  or  25  per  cent  solution  of  sodium  hydroxide. 
The  containing  jar  is  porcelain.  The  zinc  plates  have  mercury 
added  to  them  during  casting,  so  that  they  are  amalgamated 
throughout.  The  copper  oxide  ^-^ 

plates  are  made  from  copper  scale 
which  is  finely  ground  and  then 
roasted  until  thoroughly  oxidized. 
The  oxidized  powder  is  then 
moistened  with  a  solution  of  so- 
dium hydroxide  and  pressed  into 
cakes  a  little  larger  than  desired 
in  the  finished  product.  These 
cakes  are  then  dried  and  baked  at 
a  bright  red  temperature,  which 

partially    Welds     the    particles    to-       FIG.  61. -Edison  Lalande  battery 

gether.  After  cooling,  the  plates  are  reduced  to  copper  at 
the  surface  by  zinc  dust,  to  make  them  conduct.  They  are 
then  washed  and  are  ready  for  use.5  The  hydroxide  solution 
is  covered  with  a  heavy  mineral  oil  to  prevent  its  creeping  up 
the  zinc  plates  and  corroding  them.  This  battery  has  an  initial 
electromotive  force  of  0.95  volt,  but  on  continuous  discharge 
at  normal  rate  it  drops  to  about  0.6  volt.  The  capacity  varies 
from  100  to  600  ampere  hours,  depending  on  the  size  of  the 
battery. 

The  Daniell  cell,  brought  out  in  1836,6  belongs  to  a  different 
class  of  cells,  in  which  there  are  two  liquids  separated  by  a 
porous  partition.  The  positive  pole  is  copper  dipping  in  a  con- 
centrated solution  of  copper  sulphate,  and  the  negative  is  zinc 
dipping  in  sulphuric  acid.  Copper  is  deposited  on  the  positive 
in  place  of  hydrogen,  thus  avoiding  polarization,  and  zinc  goes 
in  solution  forming  zinc  sulphate.  The  electromotive  force  of 
this  cell  is  about  1.1  volt. 

The   gravity  cell,  Figure  62,  is  a  form   of  the  Daniell  cell 
5  Private  communication  from  the  company.         6  Wiedemann,  I.e.  p.  859. 


146 


APPLIED    ELECTROCHEMISTRY 


FIG.  62.  —  The  gravity  cell 


patented  by  Varley  in  1854,  but  which  did  not  become  generally 
known  until  1884.  It  is  now  the  principal  commercial  form  of 
the  Daniell  cell.7  The  gravity  cell  derives  its  name  from  the 
way  in  which  the  two  solutions  are  prevented  from  mixing. 
At  the  bottom  of  a  glass  jar  is  a  horizontal  copper  electrode 

covered  with  cop- 
per sulphate  crys- 
tals and  a  saturated 
solution  of  copper 
sulphate.  On  this 
solution  is  care- 
fully poured  a  di- 
lute sulphuric  acid 
solution,  in  which 
a  horizontal  zinc  electrode  is  immersed.  When  in  use  the 
migration  of  the  copper  ions  towards  the  cathode  prevents  their 
reaching  the  zinc,  while  if  the  cell  stands  on  open  circuit  the 
copper  sulphate  would  finally  reach  the  zinc  by  diffusion  and 
cover  it  with  a  layer  of  copper.  This  cell  should  therefore  al- 
ways be  kept  on  a  closed  circuit  through  a  few  ohms  resistance. 
Dry  cells  are  a  type  of  primary  battery  that  have  recently 
come  into  very  general  use.  It  is  estimated  that  50  million 
a  year  are  manufactured  in  the  United  States,  a  large  majority 
of  which  are  of  a  standard  size,  cylindrical  in  shape,  15  centi- 
meters long  and  6.25  centimeters  in  diameter.8  They  are 
essentially  Leclanche  cells  with  a  very  small  quantity  of  elec- 
trolyte. Their  greatest  field  of  usefulness  is  probably  tele- 
phony and  next  the  ignition  through  spark  coils.9 

The  container  or  outside  insulation  is  usually  pasteboard, 
sometimes  waterproofed  by  paraflfine  or  pitch.  Just  inside  of 
the  container  is  the  cylindrical  zinc  negative  pole,  usually  15 
centimeters  high,  6.25  in  diameter,  and  0.3  to  0.55  millimeters 
thick.  Lining  the  zinc  on  the  inside  is  a  layer  of  a  special 
grade  of  pulp  board,  moistened  with  a  solution  of  zinc  and 

i  Schneider,  I.e.  p.  54. 

8  D.  L.  Ordway,  Trans.  Am.  Electrochem.  Soc.  17,  341,  (1910). 

»  Burgess  and  Hambuechen,  Trans.  Am.  Electrochem.  Soc.  16,  97,  (1909). 


PRIMARY   CELLS  147 

ammonium  chlorides.  The  zinc  chloride  is  added  for  reducing 
the  local  action.  Inside  the  pulp  board  containing  the  electro- 
lyte are  placed  the  depolarizer  and  the  positive  pole.  The  de- 
polarizer is  manganese  dioxide,  mixed  with  carbon,  graphite,  or 
a  mixture  of  both.  Graphite  is  used  to  give  the  cell  a  lower 
resistance.  A  carbon  rod  at  the  center  and  surrounded  by  this 
mixture  is  the  positive  pole.  An  average  composition  of  this 
filling  mixture  is  the  following : 9 

10  parts  of  manganese  dioxide, 

10  parts  of  carbon  or  graphite,  or  both, 

2  parts  of  ammonium  chloride, 

1  part  of  zinc  chloride. 

Sufficient  water  is  added  to  give  a  proper  amount  of  electro- 
lyte to  the  cell,  depending  on  the  original  dryness  of  the  ma- 
terials, their  fineness,  the  quality  of  the  paper  lining,  and 
similar  factors.  The  usual  specifications  for  the  manganese 
dioxide  are  that  it  shall  contain  85  per  cent  of  the  dioxide  and 
less  than  1  per  cent  of  iron.  The  cell  is  sealed  up  on  top 
with  a  pitch  composition  to  hold  in  the  filling  material  and  to 
prevent  the  cell  from  drying.  The  carbon  rod  extends  above 
the  seal  and  is  provided  with  a  binding  screw. 

The  electromotive  force  of  this  cell  is  between  1.5  and  1.6 
volts.  On  a  short  circuit  through  an  ammeter,  a  cell  will  give 
from  18  to  25  amperes.  The  energy  output  of  a  cell  of  the 
dimensions  given  above,  discharged  to  0.2  volt  continuously, 
varies  from  about  20  watt  hours  when  discharged  through 
2  ohms  to  57  watt  hours  when  discharged  through  40  ohms.8 

The  primary  cells  described  above  are  comparatively  unim- 
portant compared  with  one  which  is  not  yet  realized,  but  on 
which  a  great  deal  of  time  and  work  has  been  spent.  This  is 
the  cell  in  which  carbon  and  oxygen  are  the  elements  con- 
sumed. The  present  method  of  producing  work  by  the  com- 
bustion of  coal  to  run  steam  engines  is  very  inefficient,  as  only 
about  15  per  cent  of  this  energy  is  obtained  as  work,  the  rest 
being  lost  as  heat.  If  it  were  possible  to  devise  a  cell  in  which 
carbon  and  oxygen  would  unite  with  the  production  of  an 


148  APPLIED   ELECTROCHEMISTRY 

electric  current  and  no  other  form  of  energy,  at  ordinary  tem- 
perature, a  much  greater  amount  of  energy  could  be  obtained. 
In  order  to  calculate10  the  free  energy,  or  energy   that   is 
obtainable  as  useful  work,  of  the  reaction  in  question, 

C  +  02=C02, 

consider  a  reaction  chamber,  as  shown  in  Figure  63,  containing 
carbon,  oxygen,  carbon  monoxide,  and  carbon  dioxide  in  equi- 


Cfe     CO     Ok 

A"t^<Y\&VVX 


FIG.  63.  —  Reaction  chamber 

librium  at  a  given  temperature.  The  chamber  has  two  pis- 
tons separated  from  it  by  semipermeable  membranes.  The 
semipermeable  membrane  at  the  end  of  the  cylinder  containing 
oxygen  is  permeable  to  oxygen  only,  and  that  at  the  end  of  the 
cylinder  containing  carbon  dioxide  is  permeable  only  to  carbon 
dioxide.  The  maximum  work  that  this  reaction  can  produce 
is  then  obtained  by  the  following  reversible  process  :  one  mole 
of  oxygen  is  admitted  to  the  oxygen  cylinder  at  atmospheric 
pressure  and  is  allowed  to  expand  reversibly  to  the  equilibrium 
pressure  of  oxygen  p0z  in  the  reaction  chamber.  The  work 
produced  is 


The  oxygen  is  then  forced  into  the  reaction  chamber  through 
the  semipermeable  membrane.  In  order  to  preserve  equi- 
librium, one  mole  of  carbon  dioxide  must  be  simultaneously 
withdrawn  at  the  equilibrium  pressure  pCOz  into  the  carbon  di- 
oxide cylinder.  The  work  produced  in  these  two  steps  is  evi- 
dently zero.  The  carbon  dioxide  must  then  be  compressed  to 
atmospheric  pressure,  in  which  step  the  work  produced  is 


10  Nernst,  Theoretische  Chemie,  6th  ed.  p.  698,  (1909). 


PRIMARY   CELLS  149 

The  sum  of  Wl  and  TF2  is  the  maximum  work  obtainable  : 

Tf,+  Wt  =  RTlog?™!.  (1) 

^o2 

It  would  be  impossible  to  measure  the  pressure  of  oxygen  in 
this  mixture  directly,  but  its  value  at  1000°  C.  can  be  obtained 
as  follows:  It  has  been  found  experimentally  that  at  1000°  C. 
carbon  dioxide  dissociates  to  0.06  per  cent,  according  to  the 
reaction : 

2  CO2  ^±  O2  +  2  CO. 

At  a  total  pressure  of  one  atmosphere,  the  equilibrium  pressures 
for  this  system  are  then : 

Carbon  dioxide 0.9991  atmosphere 

Carbon  monoxide      ....  0.0006  atmosphere 
Oxygen        .......  0.0003  atmosphere 

Substituting  in  the  equation  for  the  mass  action  law, 

K(Pco.^  =  Pos(pco)*,  (2) 

K  (I)2  =  (0.0003)(0.0006)2.  (3) 

It  has  also  been  found  that  at  1000° C.  and  atmospheric  pressure 
an  equilibrium  mixture  of  carbon  monoxide  and  dioxide  in  the 
presence  of  carbon  has  the  following  pressures : 

Carbon  monoxide      ....  0.993  atmosphere 
Carbon  dioxide 0.007  atmosphere 

Since  jfiTis  known  from  equation  (3),  the  pressure  of  oxygen  in 
this  system  can  be  computed  by  substituting  in  equation  (2) : 
JT(0.007)2  =  z  (0.993)2. 

From  this,  x  =  5.4  x  10~15  atmosphere. 
Substituting  in  equation  (1), 

Trl+TT2=  1273  7?  log  540x00^_16 

=  70600  calories  at  1000°  C. 

This  gives  the  free  energy  of  the  reaction  at  1000° C.,  and  it  may 
be  found  at  room  temperature  as  follows :  The  heat  of  the 
reaction  at  room  temperature  is  Q  =  97650  calories,  and  it  would 
be  approximately  the  same  at  the  absolute  zero,  on  account  of 


150  APPLIED   ELECTROCHEMISTRY 

the  small  change  in  the  heat  capacity  of  carbon  and  oxygen 
before  and  after  uniting.  This  would  also  be  the  free  energy 
at  the  absolute  zero,  since  free  energy  and  the  total  energy  of  a 
.reaction  are  equal  at  this  temperature.  The  free  energy  at  the 
absolute  temperatures  1273°  and  0°  being  known,  it  may  be 
interpolated  for  20°  by  the  formula, 

Fi  +  TT2  =  97650  -  9765°  "J0600  x  293 

1.273 

=  91470  calories  at  20°  C. 

The  ratio  of  the  free  to  the  total  energy  is  therefore  approxi- 
mately |i*-,  corresponding  to  94  per  cent. 

If  the  carbon  of  the  carbon  electrode  enters  the  electrolyte  as 
an  ion  with  four  positive  charges,  and  the  oxygen  as  an  ion  with 
two  negative  charges,  the  electromotive  force  of  this  cell  would 
be  found  from  the  equation, 

4  .EF=  91000  calories  ; 


from  which  E  =  =  0.99  volt. 

4  x  23100 

The  difficulties  in  realizing  this  cell  consist  in  finding  an  elec- 
trolyte in  which  carbon  will  dissolve,  and  in  making  an  oxygen 
electrode.  So  far  they  have  been  insuperable,  and  at  present 
there  seems  very  little  prospect  of  success. 

Attention  has  been  called  by  Ostwald  n  to  an  important  point 
in  this  cell,  that  the  carbon  and  oxygen  must  form  the  opposite 
poles  of  the  cell  and  must  act  on  each  other  through  an  inter- 
vening electrolyte.  If  the  carbon  and  oxygen  acted  directly  on 
each  other,  local  action  would  result,  and  no  current  would  be 
produced. 

A  number  of  attempts  have  been  made  to  make  a  carbon 
oxygen  cell,  all  of  which  employed  some  fused  salt  or  hydrate  as 
electrolyte.  This  is  a  disadvantage  to  start  with,  for  energy 
will  be  lost  by  radiation  in  keeping  the  cells  at  a  temperature  of 
several  hundred  degrees  centigrade.  One  of  the  first  of  these 
attempts  was  made  by  Jablochkoff12  in  1877.  In  this  cell  the 

11  Z.  f.  Elektroch.  1,  122,  (1894). 

12  E.  de  Fodor,  Elektricitat  direkt  aus  Kohle,  p.  41,  (1807). 


PRIMARY   CELLS  151 

carbon  was  dipped  into  melted  potassium  nitrate,  and  the  posi- 
tive electrode  was  iron.  This  cell  could  never  be  successful, 
for  the  carbon  is  brought  directly  in  contact  with  the  oxidizing 
substance.  Also,  the  oxygen  was  not  taken  directly  from  the 
air,  but  was  in  the  expensive  form  of  a  nitrate. 

In  1896,  W.  W.  Jacques  patented  a  cell  which  excited  a 
good  deal  of  interest  at  that  time.  This  consisted  of  an  iron 
pot  containing  a  melted  mixture  of  potassium  and  sodium 
hydrate,  into  which  a  carbon  rod  dipped  ;  air  was  blown  against 
the  iron  pot,  which  formed  the  positive  pole,  the  idea  being  that 
this  oxygen  would  combine  with  the  carbon  through  the  inter- 
vening electrolyte  and  produce  a  current.  It  is  evident  that 
the  hydrate  would  be  changed  to  carbonate  and  that  some 
method  would  have  to  be  used  to  regenerate  it.  The  carbon 
was  in  the  expensive  form  of  electrodes.  There  was  a  certain 
amount  of  direct  oxidation  of  the  carbon,  for  the  air  also  came 
in  direct  contact  with  the  hot  carbon  electrode.  For  these 
and  other  reasons  this  cell  has  not  been  a  success. 

In  conclusion,  it  may  be  said  that  the  chance  of  finding  any 
solvent  in  which  carbon  would  dissolve  as  ions  is  very  remote, 
and  to  find  one  in  which  both  oxygen  and  carbon  would  thus 
dissolve  is  still  more  remote  ;  consequently  it  seems  hardly 
possible  that  this  problem  will  be  solved  by  such  a  direct 
method. 


CHAPTER   IX 
THE  LEAD  STORAGE  BATTERY 

1.    HISTORY  AND  CONSTRUCTION 

THE  lead  storage  battery  in  the  charged  state  consists  of 
a  positive  plate  of  lead  peroxide  and  a  negative  plate  of  finely 
divided  lead,  both  dipping  in  sulphuric  acid  of  about  1.2  specific 
gravity.  When  discharged,  the  surface  of  both  plates  has  been 
changed  to  lead  sulphate.  The  plates  may  be  brought  back 
to  their  original  condition  by  sending  a  current  through  the 
battery  in  the  reverse  direction. 

This  battery  was  invented  in  1860  by  Gaston  Plante.1  The 
original  battery  consisted  of  two  lead  plates  separated  by 
flannel  and  rolled  together,  and  immersed  in  sulphuric  acid. 
The  flannel  was  soon  replaced  by  thin  strips  of  rubber,  on 
account  of  its  being  eaten  away  by  the  acid.  The  battery 
was  charged  from  two  Bunsen  elements  in  opposite  directions 
six  or  eight  times  on  the  first  day,  allowing  the  cell  to  discharge 
itself  between  each  change  in  direction  of  charging.  It  was 
noticed  that  the  period  of  discharge  continued  to  increase 
regularly.  The  period  during  which  the  battery  was  sub- 
mitted to  the  action  of  the  current  in  the  same  direction  was 
then  increased,  and  the  battery  was  allowed  to  rest  for  eight 
days,  after  which  it  was  charged  in  the  opposite  direction. 
The  period  of  rest  was  then  extended  to  two  weeks,  one  month, 
two  months,  and  so  on,  and  the  duration  of  discharge  continued 
to  increase.  When  sufficient  capacity  was  reached,  the  plates 

1  Gaston  Plant^,  The  Storage  of  Electrical  Energy,  p.  30,  (1887). 

152 


THE  LEAD  STORAGE  BATTERY  153 

were  considered  formed,  and  the  charging  current  was  then 
always  sent  through  the  cell  in  the  same  direction.  The  reason 
a  thick  layer  of  peroxide  cannot  be  produced  in  one  charge  is 
that  it  conducts  the  current  and  prevents  the  lead  below  it  from 
being  attacked. 

It  is  evident  that  this  method  of  formation  would  be  very 
expensive.  To  overcome  this  difficulty,  Metzger  and  Faure, 
independently  and  approximately  simultaneously,  devised 
methods  of  applying  the  active  material  to  the  plate  in  the  form 
of  lead  oxides.  This  method  was  patented  by  Faure  2  in  1880, 
and  has  since  been  known  by  his  name.^  Faure's  original  method 
of  applying  the  oxides  was  to  coat  the  plate  with  a  paste  made 
of  the  material  and  to  hold  it  in  place  by  means  of  some  porous 
material,  such  as  felt  or  asbestos  paper. 

Charles  F.  Brush  of  Cleveland  applied  for  a  patent  covering 
this  same  field  about  a  month  before  Faure,  and  the  patent  was 
finally  awarded  to  him.  Eventually  all  of  the  essential  patents 
were  acquired  by  the  Electric  Storage  Battery  Company  of 
Philadelphia.3 

The  two  general  methods  of  making  storage  battery  plates 
now  in  use  are  only  modifications  of  the  original  Plante  or 
Faure  process. 

The  Plante  process  includes  all  methods  in  which  the  active 
material  is  made  from  the  plate  itself,  which  must  be  of  pure 
soft  lead.4  Formation  is  accelerated  in  a  number  of  ways. 
Usually  the  first  operation  is  to  work  up  the  surface  mechanically 
by  cutting  grooves,  unless  it  is  cast  in  this  form.  The  next 
operation  is  to  produce  the  necessary  amount  of  active  material. 
This  is  frequently  done  by  allowing  the  plates  to  stand  for  a 
certain  time  in  some  corroding  solution  of  acids  that  produces 
a  thick  layer  of  lead  sulphate.  This  may  then  be  reduced 
electrolytically  to  lead  or  oxidized  to  lead  peroxide.  The  acids 
other  than  sulphuric  must  be  thoroughly  washed  out  before  the 
battery  is  ready  for  use.  For  example,  a  mixture  of  nitric  and 

2  U.  S.  Patents  252,002,  (1882)  and  309,939,  (1884). 
8  Watson,  Storage  Batteries,  p.  10,  (1908). 
4  Watson,  I.e.  p.  21. 


154  APPLIED   ELECTROCHEMISTRY 

sulphuric  acids  would  have  this  effect  of  producing  a  layer  of 
sulphate.  The  other  method  of  rapid  Plante  formation  is 
entirely  electrolytic,  according  to  the  following  principle  : 

The  plate  is  electrolyzed  as  ail  anode,  but  lead  peroxide, 
which  would  protect  the  plate  from  further  action,  is  prevented 
from  forming  by  adding  some  salt  or  acid  to  the  solution,  the 
anion  of  which  separates  at  a  lower  potential  than  the  peroxide 
ion  and  causes  the  production  of  sulphate.  Lead  sulphate  does 
not  conduct,  so  the  current'  has  to  penetrate  to  the  lead  below, 
and  as  much  sulphate  may  be  produced  in  one  step  as  is  desired. 
Such  additions  are  acetates,  tartrates,  chlorides,  nitrates,  chlo- 
rates, perchlorates,  and  the  corresponding  acids. 

Peroxide  is  not  always  formed  on  a  lead  anode  in  sulphuric 
acid,  even  when  no  substance  is  added  to  the  solution  to  prevent 
it,  as  is  shown  by  the  fact  that  the  lead  plate,  which  is  the 
anode,  on  discharging,  becomes  covered  with  sulphate.  If 
therefore  a  lead  plate  is  short  circuited  in  a  solution  of  sul- 
phuric acid  with  a  peroxide  plate,  it  will  become  covered  with 
sulphate,  proportional  in  amount  to  the  current  that  flows 
through  the  plate.5 

In  the  Faure  batteries  the  plates  for  holding  the  active  ma- 
terial consist  of  lead  with  about  5  per  cent  of  antimony. 
The  active  material  is  made  by  making  a  paste  of  lead  oxide 
and  sulphuric  acid  and  applying  it  to  grooves  cast  in  the  sup- 
porting grid.  This  paste  sets  and  becomes  hard,  after  which  it 
is  changed  to  lead  sponge  and  peroxide  by  electrolysis  in  a  solu- 
tion which  may,  or  may  not,  be  sulphuric  acid. 

The  negative  plates  of  the  chloride  battery,  formerly  made 
by  the  Electric  Storage  Battery  Company  of  Philadelphia,  but 
given  up  about  eight  years  ago,6  were  made  in  an  entirely  dif- 
ferent way.  Lead  and  zinc  chlorides  were  melted  together  and 
poured  into  the  supporting  grid.  The  zinc  chloride  was  then 
dissolved  in  water,  leaving  the  lead  chloride  in  a  porous  condi- 
tion. This  was  then  reduced  to  sponge  lead  electrolytically. 
The  positive  plates  of  this  battery  were  made  by  the  Plante 

6  Dolezalek,  The  Theory  of  the  Lead  Accumulator,  p.  194. 
6  Private  communication  from  the  company. 


THE  LEAD  STORAGE  BATTERY 


155 


process.     Though  the  method  is  no  longer  employed,  the  name 
is  retained.     Figure  64  shows  the  positive  and  negative  plates 


FIG.  04.  —  Positive  and  negative  plates  of  the  chloride  accumulator 

of  one  type  of  the  so- called  chloride  accumulator.  The  positive 
,plate  contains  buttons  of  lead  strips  wound  up  and  held  in  a 
grid.  In  the  negative  plate  the  active  material  is  held  in  posi- 


niiniui 

juuuwuuuum 


m 
w 


FIG.  Go  -  The  Gould  battery  plate 


156 


APPLIED   ELECTROCHEMISTRY 


tion   by  perforated  sheet  lead,  while  the  positive  plate  is  of 
the  Plante  type. 

In  the  Gould  battery,  both  plates  are  made  by  the  Plante 
method.  A  pure  lead  sheet  is  stamped  out,  and  the  surface  is 
worked  up  into  the  shape  shown  in  cross  section  in  Figure  65, 
by  rolling  the  surface  a  number  of  times  with  steel  disks. 
This  process  is  called  spinning.  An  unspun  portion  of  the 
plate  is  left  where  the  wheels  stop,  forming  a  number  of  cross- 
bars in  each  plate.  A  thin  layer  of  lead  peroxide  is  then  pro- 
duced by  an  electrolytic  process.  Negative  plates  are  made  by 


FIG.  (Hi.  —Positive  Gould  plate 

reducing  peroxide  plates.7     Figure  66  shows  a  positive  plate 
ready  to  be  formed. 

7  Catalogues  Of  the  Gould  Company. 


THE  LEAD  STORAGE  BATTERY  157 

There  are  a  large  number  of  different  types  of  batteries  made 
by  different  companies,  information  concerning  which  is  best 
obtained  from  their  catalogues. 

2.    THEORY  OF  THE  LEAD  STORAGE  BATTERY1 

The  theory  of  the  lead  storage  battery  now  generally  ac- 
cepted is  known  as  the  sulphate  theory,  and  is  due  to  Gladstone 
and  Tribe.  According  to  this  theory  sulphuric  acid  combines 
with  the  plates  on  discharge,  and  is  set  free  on  charge.  On 
discharge  hydrogen  is  deposited  on  the  lead  peroxide  and  re- 
duces it  to  lead  oxide,  which  is  changed  to  lead  sulphate.  This 
is  represented  by  the  equation  : 

Pb02  +  H2  +  H2S04  =  PbS04  +  2  H20.  (1) 

At  the  same  time  the  sulphate  radical  is  deposited  on  the  lead 
plate  and  changes  it  to  lead  sulphate  : 

Pb+SO4  =  PbS04.  (2) 

The  total  change  in  the  storage  battery  on  discharge  is  the 
sum  of  equation  (1)  and  (2): 

Pb02  +  Pb  +  2  H2S04  =  2  PbS04  +  2  H20.  (3) 

In  the  discharged  state  both  plates  are  covered  with  sulphate. 
On  charging,  the  reaction  on  the  positive  plate  is : 

PbSO4  +  S04  +  2  H20  =  Pb02  +  2  H2S04 ;  (4) 

and  in  the  negative  plate : 

PbSO4  +  H2  =  Pb  +  H2SO4.  (5) 

The  sum  of  equations  (4)  and  (5)  represents  what  takes 
place  in  the  whole  battery  on  charging : 

2  PbS04  +  2  H20  =  Pb02  +  Pb  +  2  H2SO4.  (6) 
Equation  (6)  is  identical  with  equation  (3)  read  from  right  to 
left.  The  changes  taking  place  both  on  discharge  and  charge 
may  therefore  be  represented  by  the  following  reversible  equa- 
tion : 

Pb02  +  Pb  +  2  H2S04  :£  2  PbS04  +  2  H20.  (7) 

1  This  discussion  is  taken  mainly  from  Dolezalek's  The  Theory  of  the  Lead 
Accumulator,  translated  by  Carl  L.  von  Ende.  John  Wiley  and  Sons,  (1904). 


158 


APPLIED   ELECTROCHEMISTRY 


From  right  to  left  this  represents  the  discharge,  and  from 
right  to  left  the  charge. 

In  order  to  show  that  this  equation  represents  what  takes 
place  in  the  lead  cell,  it  is  necessary  to  show  that  the  formation 
or  disappearance  of  each  of  the  substances  involved  is  propor- 
tional to  the  amount  of  electricity  that  has  passed.  It  must 
also  be  shown  that  the  substances  involved  are  those  given  in 
the  equation. 

That  the  charged  positive  plate  is  the  peroxide  of  lead  and 
not  some  other  oxide  or  hydrate  was  shown  by  measuring  the 
electromotive  force  of  different  lead  oxides  and  hydrates  on 
lead  against  a  zinc  electrode  and  comparing  with  a  charged 
positive  plate.  The  results  were  the  following : 


Pb 
Pb 
Pb 
Pb 
Pb  |  Pb02 


Pb20 
PbO 
Pb304 
H2PbO, 


-  Zn  =  0.42  volt 

-  Zn  =  0.46  volt 

-  Zn  =  0.75  volt 

-  Zn  =  0.96  volt 
—  Zn  =  2.41  volts 


1.15 


A  charged  positive  plate  has  a  potential  of  2.4  volts,  showing 
that  lead  peroxide  is  the  compound  that  exists  on  the  positive 
plate. 

Gladstone  and  Tribe  showed,  by  analyzing  the  active  mass 
of  the  plates  at  different  stages  of  charge  and  discharge,  that 
the  production  of  sulphate  on  each  plate  is  proportional  to  the 

quantity  of  electricity 
that  has  been  taken 
from  the  cell. 

The  same  thing  was 
shown  by  W.  Kohl- 
rausch  and  C.  Heim 
by  measuring  the 
specific  gravity  of  the 
acid  on  charge  and 
o  10  20  30  40  so  eo  discharge.  The  den- 

AMPERE  HOURS  .,  i  '    -•  .  -. 

sity  changed  exactly 

FIG.  67.  —  Change  in  density  of  acid  with  charge  and   .     J  .  J 

discharge  in  proportion  to   the 


1.11 


THE  LEAD  STORAGE  BATTERY  159 

quantity  of  electricity  that  had  passed  through  the  cell,  as 
shown  in  Figure  67.  A  calculation  of  the  change  in  specific 
gravity  by  means  of  equation  (7)  agrees  with  that  found. 
This  calculation  is  as  follows : 

The  uncharged  battery  contained  3350  cubic  centimeters  of 
acid  of  1.115  specific  gravity,  corresponding  to  16.32  per  cent 
acid.  The  total  solution  therefore  weighed 

3350  x  1.115  =  3735  grams, 
and  contained 

0.1632  x  3735  =  610  grams  of  acid, 
and  therefore  3125  grams  of  water. 

After  charging  with  50  ampere  hours,  according  to  equation 
(7),  the  amount  of  water  that  disappeared  was 
50  x  2  x  0.336  =  33.6  grams, 
and  the  amount  of  sulphuric  acid  formed  was 
33.6  x  f|  =  183  grams. 
The  solution  therefore  contained  after  charging 

3125  -  33.6  =  3091.4  grams  of  water,  and 

610  -|-  183  =  793  grains  of  sulphuric  acid. 

The  total  weight  was  therefore  3884  grams,  and  the  amount 
of  sulphuric  acid  contained  was  -ggfa  X  100  =  20.42  per  cent, 
corresponding  to  a  density  of  1.146.  The  observed  density 
was  1.147. 

In  order  to  see  whether  the  heat  of  the  reaction  of  equation 
(7)  and  the  electromotive  force  of  the  cell  are  in  agreement, 
the  heat  of  the  reaction  may  be  substituted  in  the  equation : 2 

E=     Q    +TB—,  (8) 

23070^      dT' 

when  E  is  the  electromotive  force  and  2  Q  is  the  heat  of  the 
reaction  of  equation  (7).  Half  of  this  value  is  used  in  equa- 
tion (8),  for  2  Q  corresponds  to  the  amount  of  material 
changed  by  the  passage  of  2  coulombs  of  electricity.  The 
value  of  Q  has  been  measured  by  Tscheltzow  and  by  Streintz, 
who  found  43,800  calories  and  42,800  calories  respectively,  for 

2  Le  Blanc,  Electrochemistry,  p.  173,  (1907). 


160 


APPLIED   ELECTROCHEMISTRY 


acid  of  a  density  1.044,  corresponding  to  0.70  mole  of  acid  per 
liter.  This  concentration  is  taken,  since  at  this  value  the  tem- 
perature coefficient  of  the  electromotive  force  is  zero.  The 
values  of  JE  computed  are 

E=  1.86  volts  (Streintz), 
j£=1.90  volts  (Tscheltzow), 

and  the  measured  value  for  this  density  of  acid  gives  1.89  to 
1.90  volts. 

For  acid  of  specific  gravity  1.15,  the  values  of  Q  are  42,600 

r)  7^ 

calories  and  43,600  calories  respectively,  and  the  value  of  — —  is 

+  0.4  x  10-3  volt.  At  17°  C.,  T=  290.  Substituting  in  equa- 
tion (8),  .#=1.96  and  2.01  volts  respectively.  The  measured 
value  is  1.99  to  2.01  volts.  This  calculation  furnishes  a  con- 
clusive proof  that  the  reaction  given  in  equation  (7)  is  the  one 
that  takes  place  in  the  lead  accumulator. 

It  is  evident  that  since  the  acid  becomes  more  dilute  on  dis- 
charging a  lead  battery,  the  electromotive  force  must  decrease 
with  decreasing  concentration.  Table  18  shows  the  relation 
between  the  concentration  of  the  acid  and  the  electromotive 
force,  from  direct  measurements. 

TABLE  18 


DENSITY  OF  H,SO4 

PER  CENT  H2SO4 

ELECTROMOTIVE  FORCE  AT  15°  C» 

1.050 

7.31 

1.906 

1.150 

20.91 

2.010 

1.200 

27.32 

2.051 

1.300 

39.19 

2.142 

1.400 

50.11 

2.330 

It  will  be  noticed  that  the  electromotive  force  of  the  lead 
storage  battery,  with  the  concentration  of  acid  ordinarily  used, 
has  the  unusually  high  value  for  a  battery  of  over  two  volts. 
Sulphuric  acid,  if  electrolyzed  between  platinum  and  electrodes, 
gives  a  weak  evolution  of  gas  at  1.7  volts  and  at  1.9  a  strong 
evolution.  If  lead  sulphate  were  spread  in  platinum,  it  would 
therefore  not  be  possible  to  reduce  it  to  lead  and  oxidize  it  to 


THE  LEAD  STORAGE  BATTERY 


161 


peroxide,  for  the  potential  required  could  not  be  reached.  On 
lead,  however,  the  overvoltage  is  so  great  that  the  gas  evolu- 
tion does  not  take  place  below  2.3  volts,  which  is  greater  than 


y-mol.  U^SOt 


FIG.  68.  —  Temperature  coefficient  of  electromotive  force  of  lead  storage  battery  a& 
function  of  the  acid  concentration 

the  voltage  needed  to  change  the  sulphate  in  lead  on  one  elec- 
trode and  peroxide  on  the  other.  If  it  were  not  for  this  high 
overvoltage  on  lead,  the  lead  storage  battery  would  be  an  im- 
possibility. 

The  temperature  coefficient  of  the  lead  storage  battery  for 
the  concentration  of  acid  used  is  positive,  but  on  decreasing  the 
concentration  of  acid  the  temperature  coefficient  falls  to  zero 
and  then  becomes  negative.  This  is  shown  by  the  curve  in 
Figure  68,  representing  the  results  of  experiments  in  which  the 
temperature  coefficient  was  determined  between  0°  and  24°  C. 
The  temperature  coefficient  is  constant  in  value  between  10° 
and  70°  C.  The  heavy  line  in  the  plot  gives  the  experimental 
results,  and  the  dotted  curve  the  values  calculated  from  equa- 
tion (8). 

The  mechanism  of  the  reactions  taking  place  in  the  lead  storage 
battery  has  been  explained  with  the  help  of  the  osmotic  theory 
by  Le  Blanc  and  by  Liebenow.  The  difficulty  in  applying  this 
theory  to  the  lead  storage  battery  is  to  know  what  are  the  ions 
in  the  case  of  the  lead  peroxide  plate.  According  'to  Le 


162  APPLIED    ELECTROCHEMISTRY 

Blanc's  theory,  the  lead  peroxide,  having,  a  definite,  though 
slight  solubility,  dissolves  in  the  dilute  sulphuric  acid  and  then 
reacts  with  water  according  to  the  equation: 

Pb02  +  2  H20  =  Pb  +  4  OH-.  (9) 

During  discharge  the  tetravalent  lead  ions  give  up  two  charges 

of  electricity  and  combine  with  the  SO4  ions  to  form  lead 
sulphate.  The  tetravalent  lead  ions  are  replaced,  as  they  are 
used  up,  by  the  solution  of  more  lead  peroxide.  There  is  no 
loss  in  free  energy  in  this  solution  and  reaction  with  water,  for 
both  of  these  reactions  take  place  at  equilibrium  concentrations. 
The  spongy  lead  electrode  is  similar  to  the  zinc  in  a  Daniell 
cell.  It  goes  in  solution  as  a  lead  ion,  but  is  precipitated  on  the 
lead  plate  because  of  the  low  solubility  of  lead  sulphate.  The 
hydrogen  ions  of  the  sulphuric  acid  combine  with  hydroxyl 
ions  of  equation  (9)  to  form  water.  The  equations  repre- 
senting the  reactions  that  take  place  subsequent  to  the  reac- 
tion of  equation  (9)  for  the  entire  battery  are  accordingly : 

Pb  +  Pb  +  2  S=04  =  2  PbS04,  (10) 

On  charge  the  reverse  of  the  above  reactions  takes  place. 
Both  the  positive  and  negative  plates  are  covered  with  lead 
sulphate,  and  the  sulphuric  acid  surrounding  the  plates  must 
also  be  saturated  with  lead  sulphate.  On  the  negative  plate 
the  lead  ions  are  deposited  as  spongy  lead,  and  on  the  positive 
plate  the  bivalent  lead  ions  are  oxidized  to  tetravalent  lead. 
The  solution  and  electrolysis  are  represented  by  the  equations: 

2  PbSO4  solid  =  2  Pb  +  2  SO4,  (12) 


2Pb=Pb  +  Pb.  (13) 

The  tetravalent  ions  then  react  with  the  hydroxyl  ions  accord- 
ing to  equation  (9)  taken  in  the  reverse  direction : 

4  H20  =  4  OH-  4-  4  H+,  (14) 

Pb  +  4  OH-  =  Pb02  +  2  H20.  (15) 


THE  LEAD  STORAGE  BATTERY  163 

The  hydrogen  ions  corresponding  to  the  hydroxyl  ions  and  the 

sulphate  ions  from  equations  (12)  unite  to  form  sulphuric  acid  : 

4  H+  +  2  S04  =  2  H2S04.  (16) 

The  sum  of  equations  (9)  to  (11)  and  of  equations  (12)  to 
(16)  will  be  found  to  result  in  equation  (7).  In  support  of 
Le  Blanc's  theory  it  may  be  stated  that  tetravalent  lead  ions  do 
exist,  and  they  are  therefore  probably  capable  of  forming  by 
the  electrolysis  of  lead  sulphate  solutions. 

Liebenow's  theory  differs  from  Le  Blanc's  only  as  to  the 
action  of  the  peroxide  electrode.  According  to  this  theory  the 
lead  peroxide  goes  into  solution  as  doubly  charged  lead  per- 
oxide ions,  so  that  the  peroxide  plate  is  to  be  considered  a 
reversible  electrode  with  respect  to  the  peroxide  ions.  On 
discharge,  the  peroxide  passes  into  the  solution  surrounding 
the  peroxide  plate,  which  is  already  saturated  with  respect  to 
these  ions.  They  then  react  with  the  hydrogen  ions  of  the 
acid  as  follows : 

PbO2  +  4  H+  =  Pb  +  2  H2O.  (17) 

The  lead  ions  then  combine  with  the  sulphate  ions  to  form 
solid  lead  sulphate  : 

Pb  +  Sl)4  =  PbSO4  solid.  (18) 

During  charge,  just  the  reverse  reactions  take  place.  The 
lead  peroxide  ions  are  deposited  on  the  positive  plate,  and  are 
replaced  as  they  are  used  up  by  the  solution  of  the  sulphate 
from  the  electrode  and  its  hydrolysis : 

Pb  +  2  H20  =  Pb02  +  4  H+.  (19) 

In  order  to  give  Liebenow's  theory  some  foundation  it  is  neces- 
sary to  prove  the  existence  of  lead  peroxide  ions.  This  was  done 
by  showing  that  on  electrolyzing  a  solution  of  lead  in  sodium 
hydroxide  the  concentration  of  the  lead  in  anode  compartment 
increased.  This  shows  that  the  sodium  plumbite  must  be  dis- 
sociated according  to  the  equation  : 

Na2PbO2  =  2  Na+  +  P~bO2.  (20) 

The  electromotive  force  of  the  lead  storage  battery  can  be 


164  APPLIED    ELECTROCHEMISTRY 

expressed  by  the  Nernst  formula  by  the  aid  of  Liebenow's 
theory.  If  PPbo2  is  the  electrolytic  solution  pressure  of  lead 
peroxide  and  PPb  that  of  lead,  and  if  the  jt?'s  refer  to  the  osmotic 
pressure  of  the  ions,  the  potential  difference  between  the  per- 
oxide plate  and  the  solution  is 

(21) 


and  between  the  lead  plate  and  the  solution  is 


e2  =  ^log^.  (22) 

2          2         8  ..  V       J 


The  electromotive  force  of  the  cell  is  therefore 

(23) 


In  confirmation  of  this  theory,  it  has  been  found,  as  would 
be  predicted  from  equation  (23),  that  in  an  alkaline  solution, 
in  which  the  concentrations  of  the  lead  and  lead  peroxide 
would  be  greater  than  in  acid  solutions,  the  value  of  E  is  less 
than  in  acid  solutions. 

The  work  obtainable  from  a  storage  battery  depends  on  its 
capacity  and  the  electromotive  force  measured  at  its  poles 
while  the  current  is  flowing.  If  V  is  the  voltage  on  charging, 
E  is  the  open  circuit  electromotive  force,  I  is  the  charging 
current,  and  R  is  the  resistance  of  the  battery,  then 

F=  E  +  IR,  (24) 

and  on  discharge 

V  =  E  -  IR.  (25) 

If  the  current  is  kept  constant  and  the  value  of  Vis  meas- 
ured at  short  intervals,  the  charge  and  discharge  curves  ob- 
tained are  of  the  form  shown  in  Figure  69.  The  value  of  V 
rises  rapidly  in  the  first  few  minutes  of  the  charge  from  2.0  to 
2.1  volts,  and  during  the  rest  of  the  charge  continues  to  rise 
slowly,  until  at  the  end  it  suddenly  rises  to  2.5  to  2.7  volts. 
During  this  period  of  rapid  rise  in  the  value  of  F",  the  cell 
begins  to  evolve  gas,  after  which  the  value  of  V  changes  only 
slightly.  On  allowing  the  battery  to  stand  on  open  circuit 


THE  LEAD  STORAGE  BATTERY 


165 


for  several  hours,  the  electromotive  force  E  falls  to  the  value 
corresponding  to  the  density  of  the  acid.  If  the  battery  is 
then  allowed  to  discharge  with  the  same  constant  value  of  the 
current  as  used  in  charging,  the  value  of  V  at  first  falls  rapidly 


Volt 
2.8 
2.6 
2.4 
2.2 
2.0 
1.8 
1.6 
1.4 
1.2 
1.0 


"0  4  Hours 

FIG.  69.  —  Charge  and  discharge  curves  of  the  lead  storage  battery 

to  1.9  volts  and  then  gradually  to  1.85  volts,  after  which  it 
decreases  more  rapidly  to  zero.  The  curves  given  in  Figure  69 
were  obtained  with  about  20  per  cent  acid  and  a  current  density 
of  about  0.005  ampere  per  square  centimeter  of  electrode  sur- 
face. With  a  greater  current  density  the  distance  between  the 
charge  and  discharge  curves  would  increase.  The  general 
character  of  the  curves  for  different  makes  of  batteries  is  the 
same,  though  for  those  having  a  thin  layer  of  active  material 
the  curves  are  more  marked,  and  for  those  having  a  thick 
layer,  they  are  more  rounded. 

From  the  fact  that  the  charging  potential  V  is  several  tenths 
of  a  volt  higher  than  the  discharging  potential  V,  as  is  shown 
in  Figure  69,  it  is  evident  there  is  a  loss  of  from  20  to  30  per 
cent  in  the  energy  stored.  It  might  seem  at  first  sight  that  it 
is  due  to  the  loss  of  energy  due  to  the  resistance  of  the  cell 
itself,  to  the  IR  value  in  equations  (21)  and  (22),  but  the 
value  of  the  resistance  of  the  cell  is  too  small  to  account  for 
such  a  large  loss.  On  open  circuit  the  resistance  of  the 


166  APPLIED    ELECTROCHEMISTRY 

smallest  cells  used  is  only  several  hundredtlis  of  an  ohm,  and 
no  large  increase  in  its  value  takes  place  when  a  current  is 
passing.  The  cause  of  this  loss  in  energy  is  the  polarization  of 
the  electrodes  caused  by  the  change  in  concentration  of  the  acid 
in  the  pores  of  the  plates.  On  charging,  acid  is  formed  in  the 
pores  of  the  plates  where  it  becomes  more  concentrated  than  in 
the  rest  of  the  battery  on  account  of  the  fact  that  diffusion 
does  not  take  place  with  sufficient  rapidity  to  equalize  it. 
Since  the  electromotive  force  of  the  battery  increases  with  the 
concentration  of  the  acid  surrounding  the  plates,  a  higher  im- 
pressed electromotive  force  will  therefore  be  necessary  in  charg- 
ing. On  discharge,  the  acid  is  used  up  in  the  plates  and 
becomes  more  dilute  than  in  the  rest  of  the  battery,  and  the 
voltage  falls  correspondingly.  The  charge  and  discharge 
curves  of  the  lead  battery  may  now  be  taken  up  in  detail. 

The  Charging  Curve.  —  On  closing  the  charging  current,  sul- 
phuric acid  is  immediately  set  free  at  both  electrodes  and  the 
electromotive  force  therefore  rises  rapidly,  as  shown  by  the 
portion  of  the  curve  AB.  The  rate  of  diffusion  increases  with 
the  difference  in  concentration  of  the  acid  on  the  plates  and  in 
the  rest  of  the  battery,  and  when  concentration  difference  has 
become  so  great  that  the  rate  of  diffusion  and  of  formation  are 
equal,  this  rapid  increase  ceases.  The  maximum  point  at  B  is 
probably  due  to  the  destruction  of  the  thin  continuous  layer  of 
sulphate  which  forms  on  the  electrodes  during  rest,  thus  reduc- 
ing the  resistance  of  the  cell.  The  slow  regular  rise  to  O  is  due 
to  the  gradual  increase  in  the  density  of  the  acid  and  also  to 
the  deeper  penetration  of  the  current  lines  into  the  active  mass 
and  the  corresponding  greater  difficulty  in  equalizing  the  acid 
concentration  by  diffusion.  The  final  rise  CD  takes  place  when 
all  of  the  lead  sulphate  on  the  surface  of  the  plates  has  been 
used  up,  and  consequently  the  sulphate  does  not  dissolve  rapidly 
enough  to  replace  that  electrolyzed  out.  Very  soon  the  lead 
and  peroxide  ions  become  so  dilute  that  the  work  necessary  to 
deposit  these  ions  is  equal  to  that  required  to  produce  hydrogen 
on  the  cathode  and  oxygen  on  the  anode.  If  allowed  to  stand 
on  open  circuit,  sulphate  diffuses  from  within  the  plate  and  brings 


THE  LEAD  STORAGE  BATTERY  167 

back  the  electromotive  force  to  the  normal  amount.  The  maxi- 
mum point  at  D  is  due  to  the  mixing  of  the  concentrated  acid 
in  the  electrodes  with  that  outside  by  the  gas  bubbles. 

The  Discharge  Curve. — In  discharge  the  acid  is  used  up  in 
immediate  proximity  to  the  electrodes,  and  this  continues  until 
the  concentration  difference  between  the  acid  on  immediate 
proximity  to  the  electrodes  and  in  the  rest  of  the  battery  has 
become  so  great  that  diffusion  just  supplies  the  quantity  used 
up.  During  this  time  the  value  of  V  falls  rapidly  along  AE* 
The  minimum  point  at  ^is  possibly  caused  by  the  formation  of 
a  supersaturated  lead  sulphate  solution.  The  solubility  of  lead 
sulphate  in  a  20  per  cent  solution  of  sulphuric  acid  decreases 
with  decreasing  concentration,  so  that  at  the  beginning  of  the 
discharge,  when  little  solid  sulphate  is  present,  a  supersaturation 
of  short  duration  is  probable,  and  the  electromotive  force  of  the 
battery  decreases  with  increasing  concentration  of  lead  ions,  as 
seen  from  equation  (23).  The  subsequent  gradual  fall  in  the 
value  of  V  represented  by  EF  is  due  to  the  gradual  decrease 
in  the  density  of  the  acid  in  the  entire  accumulator,  but  more 
especially  to  the  greater  difficulty  in  the  acid  diffusing  deeper 
into  the  plate  as  the  current  penetrates  deeper.  Finally  the 
rate  at  which  the  acid  diffuses  cannot  supply  the  acid  used  up 
by  the  action  of  the  current,  and  the  value  of  V1  falls  off 
rapidly. 

According  to  this  explanation,  the  loss  in  energy  on  charge 
and  discharge  is  due  entirety  to  the  concentration  changes  that 
take  place  in  the  electrolyte  within  the  active  mass.  The 
smaller  these  concentration  changes  are,  the  more  nearly  will 
the  accumulator  approach  complete  reversibility.  This  is  il- 
lustrated in  Figure  70.  These  curves  were  obtained  with 
accumulator  of  200  ampere  hours  capacity.  It  is  seen  that  for 
a  current  of  0.1  ampere,  corresponding  to  a  current  density  of 
0.0017  ampere  per  square  decimeter,  the  charging  and  dis- 
charging potential  differ  by  only  0.006  volt,  or  0.3  per  cent  of 
the  electromotive  force  of  the  cell,  and  that  by  reducing  the 
current  this  loss  may  be  still  further  reduced. 

This  loss  is  not  distributed  equally  between  the  two  plates. 


168 


APPLIED    ELECTROCHEMISTRY 


The  porosity  of  the  lead  plate  made  from  the  same  sulphate 
paste  as  the  peroxide  is  about  1.4  times  as  great  as  the  peroxide, 
the  potential  of  the  peroxide  plate  falls  off  about  1.6  times 
more  than  the  lead  plate  for  a  given  change  in  the  concentni- 


Volt 


2.080 


2.078 


2.076 


2.074 


C.C5 


0.1  Amp. 


FIG.  70.  —  Pole  potential  of  the  lead  storage  battery  on  charge  and  discharge  as  a 
function  of  the  current 

tion  of  the  acid,  and  finally  the  concentration  change  on  the 
peroxide  plate  is  greater  than  on  the  lead,  because  not  only  is 
sulphuric  acid  used  up  on  discharge,  but  water  is  also  formed. 
All  of  these  facts  tend  to  make  the  loss  on  the  peroxide  plate 
greater  than  that  on  the  lead  plate.  When  the  positive  and 
negative  plates  are  made  of  similar  frames  and  paste,  and  have 
approximately  the  same  capacity,  it  has  been  found  that  60  to 
70  per  cent  of  the  loss  takes  place  on  the  peroxide  plate. 

The  capacity  of  an  accumulator  in  actual  practice  means  the 
number  of  ampere  hours  that  can  be  taken  from  it  if  discharged 
to  about  nine  tenths  of  its  original  electromotive  force,  the  point 
where  the  rapid  falling  off  in  the  electromotive  force  takes  place. 
The  capacity  therefore  is  determined  by  the  rate  of  discharge, 
for  the  smaller  the  current  the  more  time  the  acid  has  to  pene- 
trate by  diffusion  deeper  into  the  plate,  when  all  of  the  active 
material  on  the  surface  has  been  used  up.  It  is  also  evident 


THE  LEAD  STORAGE  BATTERY  169 

that  the  conductivity  of  the  acid  will  affect  the  capacity,  for  the 
higher  the  conductivity  the  deeper  will  the  current  lines  be  able 
to  penetrate  into  the  plate.  Since  there  is  a  density  of  sul- 
phuric acid  at  which  there  is  a  maximum  conductivity,  it  would 
be  expected  that  the  capacity  of  a  lead  storage  battery  would 
have  a  maximum  value  for  this  density,  and  this  has  been  shown 
experimentally  to  be  the  case. 

The  current  efficiency  of  a  lead  storage  battery,  or  the  ratio 
of  the  number  of  ampere  hours  obtainable  on  discharge  to  the 
number  put  into  the  battery  on  charge,  is  from  94  to  96  per 
cent.  The  small  loss  of  4  to  6  per  cent  is  due  to  self-discharge 
and  to  the  small  amount  of  gasing  that  cannot  be  avoided. 
The  energy  efficiency,  on  the  other  hand,  which  is  the  ratio  of 
the  energy  obtainable  in  the  external  circuit  on  discharge  to  the 
energy  put  into  the  battery  on  charge,  is  only  from  75  to  85  per 
cent.  The,  cause  of  this  comparatively  low  value,  as  explained 
above,  is  the  difference  between  the  charge  and  discharge  po- 
tential. The  loss  in  voltage  due  to  the  internal  resistance  is 
only  about  3  per  cent  with  the  usual  acid  concentration  and 
current  density.  The  loss  due  to  polarization  is  a  minimum 
when  the  conductivity  of  the  acid  in  the  battery  is  a  maximum, 
for  in  that  case  the  lines  of  current  spread  over  a  larger  surface 
by  penetrating  deeper  into  the  plate. 

If  a  battery  is  allowed  to  stand  on  open  circuit  after  charg- 
ing, the  electromotive  force  falls  in  fifteen  or  twenty  minutes  to 
the  value  corresponding  to  the  density  of  the  acid.  This  is 
due  to  solution  around  the  plates  becoming  saturated  with  lead 
sulphate.  On  discharge,  when  the  voltage  has  fallen  below  the 
value  corresponding  to  the  density  of  the  acid,  standing  on  open 
circuit  brings  it  back  to  the  normal  value.  In  this  case  the 
recovery,  as  it  is  called,  is  due  to  the  diffusion  of  the  sulphuric 
acid  into  the  pores  of  the  plate -where  it  has  become  exhausted. 

If  a  charged  cell  is  allowed  to  stand  idle,  the  density  of  the 
acid  slowly  decreases,  and  the  amount  of  electricity  obtainable 
from  it  becomes  less  from  day  to  day.  This  is  known  as  self- 
discharge,  and  for  a  cell  in  good  condition  amounts  to  from  one 
to  two  per  cent  a  day  ;  if  the  acid  contains  impurities,  however, 


170 


APPLIED   ELECTROCHEMISTRY 


it  may  amount  to  50  per  cent  a  day.  The  self -discharge  of  the 
lead  sponge  plate  is  more  likely  to  take  place  than  that  of  the 
peroxide  plate,  as  it  is  affected  by  a  greater  number  of  causes. 
It  is  fatal  for  the  lead  plate  if  the  acid  contains  any  metal  more 
electronegative  than  lead  in  contact  with  sulphuric  acid,  such 
as  platinum  or  gold,  for  the  impurity  would  be  precipitated  on 
the  plate  and  produce  a  short-circuited  local  element.  The 
lead  would  then  tend  to  dissolve  and  deposit  hydrogen  on  the 
impurity.  If  the  over-voltage  of  the  impurity  is  not  too  great, 
this  would  in  fact  take  place,  and  the  lead  plate  would  be 
changed  to  sulphate.  Now  the  potential  of  the  cell: 

Pb  sponge  |  Sulphuric  acid  |  Platinized  Pt  -f-  H2 
is  0.33  volt,  hydrogen  being  the  positive  pole.  A  current  could 
be  taken  from  this  cell  on  closing  the  external  circuit ;  lead 
sulphate  would  be  formed  on  the  lead  pole  and  hydrogen  would 
be  deposited  on  the  positive  pole.  But  if  some  metal  were 
substituted  for  platinum  for  which  the  over- voltage  is  0.33  volt 
or  more,  evidently  hydrogen  could  not  be  liberated,  and  no 
action  would  take  place.  Consequently  only  the  metals  stand- 
ing on  the  left  in  the  following  table  would  be  dangerous  for 
the  accumulator ;  those  on  the  right  could  exist  as  impurities 
in  the  acid  without  the  least  danger,  even  though  some  of  them 
are  more  electro-negative  than  lead. 


OVER- 
VOLTAGE 

OVER- 
VOLTAGE 

Platinized  Platinum   . 

0.005 

Palladium 

0.46 

Gold    

0.02 

Cadmium 

0  48 

Iron     .           .                ... 

0.08 

Tin 

0  53 

Platinum,  polished 

0.09 

Lead  

0.64 

0.15 

Zinc  

0.70 

Nickel      

0.21 

Mercury      .... 

0.78 

0.23 

As  seen  from  this  table,  platinum  is  the  most  injurious  impu- 
rity. It  has  been  found  that  one  part  of  platinum  in  a  million 
of  acid  will  produce  a  rapid  self-discharge  of  the  lead  plate. 


THE  LEAD  STORAGE  BATTERY  171 

It  has  been  found,  however,  that  metals  when  present  together 
can  produce  a  rapid  self -discharge,  which  alone  cause  scarcely 
any  action.  An  explanation  of  this  cannot  be  given  at  present. 

Contamination  by  platinum  can  easily  occur  when  sulphuric 
acid  is  used  that  has  been  concentrated  in  platinum  retorts, 
and  plates  once  contaminated  cannot  be  made  available  again. 
All  other  metallic  contaminations,  if  present  only  in  traces, 
become  inactive  on  continued  use  of  the  cell,  probably  by 
gradually  alloying  with  the  lead. 

The  self-discharge  of  the  positive  plate  takes  place  more 
slowly  than  that  of  the  lead  sponge  plate.  Metallic  impurities 
are  of  no  effect  on  the  lead  peroxide,  for  they  would  not  be 
precipitated  on  it.  The  only  kind  of  spontaneous  discharge  is 
due  to  local  action  between  the  peroxide  and  the  lead  of  the 
support,  which  together  form  a  short-circuited  element,  and 
this  is  of  importance  only  for  plates  with  a  thin  layer  of  per- 
oxide. 

Another  cause  of  self-discharge  of  a  battery  is  the  presence 
of  salts  of  metals  that  can  exist  in  more  than  one  stage  of  oxi- 
dation. For  example,  an  iron  salt  would  be  oxidized  to  the 
ferric  state  on  the  lead  peroxide,  and  would  then  diffuse  to  the 
lead  plate  and  oxidize  it  to  sulphate,  thus  gradually  discharg- 
ing both  plates. 

Sulphating.  —  The  plates  of  a  strongly  discharge  battery  on 
standing  gradually  become  covered  with  a  white  coat  of  lead 
sulphate.  If  we  attempt  to  recharge  the  battery,  it  is  found 
that  the  internal  resistance  has  considerably  increased,  and  it 
does  not  begin  to  diminish  until  the  charging  current  has 
passed  through  the  cell  for  some  time;  it  then  gradually  ap- 
proaches its  normal  value.  A  test  of  the  capacity  would  show 
that  this  has  lost  considerably  in  value.  The  phenomenon  just 
described  is  known  as  sulphating.  This  is  not  a  very  suitable 
term,  since  in  every  discharge  sulphate  is  formed  on  the  plates, 
which  is  changed  back  into  peroxide  and  lead  without  any  diffi- 
culty. Elbs  explains  sulphating  as  follows :  During  discharge 
there  is  formed  on  every  particle  of  lead  or  peroxide  a  thin 
layer  of  finely  divided  sulphate  in  contact  with  an  acid  solution 


172  APPLIED    ELECTROCHEMISTRY 

saturated  with  the  sulphate.  If  the  accumulator  is  allowed  to 
stand  in  this  condition,  and  is  subject  to  any  variation  in  tem- 
perature, the  large  crystals  will  grow  at  the  expense  of  the 
smaller  ones,  for  the  sulphate  increases  in  solubility  as  the  tem- 
perature rises,  and  the  smaller  crystals  would  be  used  up  first, 
both  on  account  of  their  size  and  because  the  solubility  of  small 
crystals  is  greater  than  that  of  large  ones.  When  the  tempera- 
ture falls,  the  sulphate  would  be  precipitated  on  the  crystals 
still  remaining,  and  in  this  way  the  plate  gradually  becomes 
covered  with  a  continuous  layer  of  lead  sulphate  crystals.  Sul- 
phating  may  be  so  bad  that  it  is  cheaper  to  replace  the  plates 
than  to  regenerate  them  by  charging. 


CHAPTER   X 
THE  EDISON  STORAGE  BATTERY 

1.    GENERAL  DISCUSSION 

THE  Edison  storage  battery  is  the  only  accumulator  besides 
the  lead  battery  that  has  any  commercial  importance.  In  this 
battery  the  active  material  of  the  positive  pole  is  an  oxide  or 
oxides  of  nickel,  and  that  of  the  negative  pole,  very  finely 
divided  iron.  The  solution  is  21  per  cent  potassium  hydrate 
with  a  small  amount  of  lithium  hydrate.1 

Edison  began  to  investigate  alkaline  accumulators  in  1898, 
and  after  trying  a  great  number  of  different  combinations  had 
the  nickel-iron  combination  fairly  well  developed  in  1900. 2 
It  fhen  passed  through  several  more  stages  of  development,  and 
arrived  in  1904  at  what  was  called  the  type  E  18  battery.  This 
had  twelve  nickel  plates  arid  six  iron  plates.  The  active  mate- 
rial of  each  plate  was  held  in  24  perforated  nickel-plated  steel 
pockets  7.5  centimeters  in  length,  1.27  centimeters  in  width, 
and  8  millimeters  in  thickness.  The  iron  plate  was  mixed 
with  mercury,  the  effect  of  which  will  be  explained  below,  and 
the  nickel  oxide  with  graphite,  to  increase  its  conductivity. 
This  battery  had  two  defects  :  (1)  the  nickel  plate  continually 
expanded  on  charging  and  did  not  contract  on  discharge,  so 
that  the  contacts  between  the  active  material  and  the  supports 
became  bad,  and  (2)  the  graphite  mixed  with  the  nickel  oxide 
gradually  disintegrated  and  did  not  fulfill  its  function  of  con- 
ducting the  current  into  the  interior  of  the  nickel  plate,  caus- 
ing the  battery  to  lose  its  capacity.1 

1  Walter  E.  Holland,  El.  World,  55,  1080,  (1910). 
2Kennelly  and  Whiting,  Trans.  Am.  Klectroch.  Soc.  6,  135,  (1904). 

173 


174 


APPLIED   ELECTROCHEMISTRY 


FIG.  71.  — Iron  electrodes  of  tlie  Edison  storage  battery 


FIG.  72.  —  Nickel  electrodes  of  the  Edison  storage  battery 


THE  EDISON  STORAGE  BATTERY  175 

Both  of  these  difficulties  seem  to  have  been  overcome  in  the 
latest  form  of  this  battery,  the  A  type,  which  has  been  on  the 
market  since  1908.  The  construction  of  the  iron  electrode, 
shown  in  Figure  71,  has  not  been  altered,  and  its  dimensions  are 
the  same  as  in  the  E  type,  but  the  nickel  electrode  has  been  con- 


FIG.  73.  —  Section  of  pencil  from  the  nickel  plate  of  the  Edison  storage  battery 

siderably  changed.  The  nickel  plate,  shown  in  Figure  72,  was 
formerly  made  just  like  the  iron  plate,  but  in  the  A  type  it 
consists  of  two  rows  of  16  round  pencils,  held  in  position  by  a 
steel  frame.  They  have  flat  flanges  at  the  ends  by  which  they 
are  supported  and  by  which  electrical  connection  is  made. 
These  pencils  are  perforated  nickel-plated  steel  tubes  filled  with 
the  active  material,  0.65  centimeter  in  diameter  and  10.5  centi- 


176  APPLIED    ELECTROCHEMISTRY 

meters  in  length.  They  are  put  together  with  a  spiral  seam  to 
resist  expansion,  and  each  cylinder  also  has  eight  steel  rings 
slipped  over  it  as  a  further  precaution.  The  graphite  is  re- 
placed by  nickel  made  into  thin  flakes,  and  distributed  in 
regular  layers  through  the  active  material,  as  shown  in  Figure 


FIG.  74.  —  Containing  can  of  the  Edison  storage  battery 

73,  a  section  of  a  pencil  taken  through  its  axis.  The  dark 
layers  are  nickel  flake,  and  the  light-colored  layers  are  the  ac- 
tive material.  A  pencil  contains  about  350  layers  of  each  kind 
of  material,  each  layer  of  active  material  being  about  0.01  inch 
thick. 

As  in  the  earlier  battery,  the  containing  can  is  of  nickel- 


THE    EDISON    STORAGE    BATTERY 


177 


plated  steel,  as  shown  in  Figure  74.  The  top  of  the  can  is 
permanently  put  in  place  after  the  plates  are  in  position. 
There  are  four  openings  in  the  top,  two  of  which  are  for  the 
terminals  bolted  to  the  groups  of  positive  and  negative  plates, 
while  the  third  is  for  filling,  and  the  fourth  contains  a  valve 
which  allows  the  gas  to  escape,  but  which  does  not  allow  any  to 
enter  from  the  outside.  The  valve  is  covered  with  a  fine  wire 
gauze  to  hold  back  any  particles  of  water  coming  off  with  the 
gas  during  charging. 

The  batteries  are  now  made  in  five  sizes.     Table  19  gives 
the  principal  facts  regarding  these  cells : 3 

TABLE  19 


TYPE 

No.  OF  POSI- 
TIVE PLATES 

NORMAL  DIS- 
CHARGE RATE. 

NORMAL  OUT- 
PUT. AMP.  II  RS. 

WT.  OF  ONE 
CELL.    KGS. 

PRICE  PER 
CELL.  DOLLARS 

AMP. 

A4 

4 

30 

150 

6.1 

13.50 

A6 

6 

45 

225 

8.7 

20.00 

A8 

8 

60 

300 

11.4 

26.00 

B2 

2 

— 

— 

— 

6.00 

JB4 

4 

— 

— 

— 

8.00 

The  average  discharge  voltage  for  any  type  is  1.2  volts,  when 
discharged  to  1  volt.  As  will  be  explained  below,  the  capacity 
can  be  considerably  increased  by  overcharging.  According  to 
the  catalogue  of  the  Edison  Storage  Battery  Company,  the 
normal  capacity  of  these  cells  can  be  increased  30  per  cent  when 
charged  at  the  normal  rate  for  ten  hours.  The  continuous  rate 
of  discharge  may  be  25  per  cent  above  the  normal  rate  without 
injury,  and  for  occasional  short  intervals  it  may  be  four  times 
the  normal  rate.  A  cell  may  stand  unused  for  any  length  of 
time  without  injury,  but  it  is  said  to  be  better  to  leave  it  dis- 
charged in  this  case.  As  stated  above,  this  must  never  be  done 
in  the  case  of  a  lead  storage  cell. 

8  Catalogue  of  the  Edison  Storage  Battery  Company,  and  a  private  communi- 
cation from  Mr.  Holland,  of  this  company. 


178  APPLIED   ELECTROCHEMISTRY 

2.   THEORY  OF  THE  EDISON  STORAGE  BATTERY  l 

The  active  material  of  the  nickel  plate  when  first  manufac- 
tured consists  of  green  precipitated  nickelous  hydroxide  com- 
pressed in  a  steel  pocket  under  hydraulic  pressure.  Since  it 
has  been  found  that  when  nickelous  hydroxide  is  oxidized 
chemically,  it  always  first  changes  to  nickel  peroxide,  NiO2,  it 
is  assumed  that  the  same  is  true  of  electrolytic  oxidation.  This 
assumption  is  justified,  for  it  offers  an  explanation  of  the  behav- 
ior of  the  nickel  plate  that  is  in  agreement  with  all  of  the  facts. 
When  the  nickelous  hydroxide  is  electrolyzed  as  anode  in  a 
potassium  hydroxide  solution,  it  therefore  first  changes  to 
nickel  peroxide.  In  fact,  analysis  shows  that  a  freshly  charged 
plate  contains  as  much  more  oxygen  than  corresponds  to  the 
formula  Ni2O3  as  would  correspond  to  at  least  8  per  cent  of 
nickel  peroxide.  The  nickel  peroxide  then  reacts  on  the  nickel- 
ous  oxide  as  follows : 

NiO2+NiO  =  Ni2O3,  (1) 

or  if  no  nickelous  oxide  is  in  immediate  contact  with  it,  it 
decomposes  of  itself : 

2NiO2  =  Ni203  +  0.  (2) 

Analysis  showed  that  the  charged  nickel  plate,. when  dried 
over  sulphuric  acid,  has  the  composition  represented  by  the 
formula  Ni2O3  •  1.3  H2O  to  Ni2O3  -  1.1  H2O.  Any  nickel 
peroxide  originally  in  the  plate  therefore  disappears  on  drying. 
It  is  of  course  impossible  to  tell  from  this  whether  the  nickel 
oxide  is  combined  with  more  water  before  drying  or  not.  In 
the  hydrates  given  above,  the  ratio  of  atoms  of  nickel  to  moles 
of  water  is  1 : 0.55  to  1 :  0.65,  while  after  the  discharge  the  ratio 
is  1 : 1.  The  nickel  plate  therefore  takes  up  water  on  discharg- 
ing, assuming  that  the  oxides  have  the  same  amount  of  water 
in  combination  while  in  the  potassium  hydrate  as  after  drying. 
The  nickelous  compound  formed  when  the  nickel  plate  dis- 
charges would 'then  be  Ni(OH)2. 

The  potential  difference  between   a  freshly  charged  nickel 

1  F.  Foerster,  Z.  f.  Elektroch.  13,  414,  (1907).  The  discussion  of  the  nickel 
plate  is  taken  from  this  article,  except  where  the  contrary  is  stated. 


THE    EDISON    STORAGE    BATTERY 


179 


plate  and  a  2.8  normal  solution  of  potassium  hydrate  is  —  0.88 
volt,  referred  to  the  dropping  electrode  as  zero.  The  negative 
sign  refers  to  the  charge  on  the  solution  surrounding  the  elec- 
trode. In  50  minutes  this  potential  difference  falls  to  —  0.86 
volt  and  in  61  days  to  —0.75  volt.  Analysis  of  this  plate 
showed  the  nickel  oxide  to  correspond  to  the  formula  Ni2O3. 
•It  was  also  found  that  the  potential  difference  of  an  electrode 
covered  electrolytically  with  nickelic  oxide  was  —0.77  volt. 
This  constant  potential  reached  by  the  charged  plate  on  stand- 
ing therefore  corresponds  to  nickelic  oxide,  and  the  potential  of  a 
freshly  charged  plate  must  be  due  to  the  nickel  peroxide.  The 
peroxide  is  not  stable,  but  gradually  decomposes  with  the 
evolution  of  oxygen,  changing  to  nickelic  oxide,  and  this  ex- 
plains the  constant  potential  arrived  at.  There  is  no  sudden 
change  when  all  the  nickel  peroxide  is  used  up,  consequently 


40 


30 


AMPERE  MINUTES,   CHARGE 
25  20  15 


10 


-0.9 


g-0.7 

I 
u 

z-0.5 


-0.3 


+  0.1 


-{-0.3 


CHARGE 


10 


80 


35 


15  20  25 

AMPERE  MINUTES,   DISCHARGE 

FIG.  75.  —  Potential  of  nickel  electrode  on  charge  and  on  discharge 


40 


180  APPLIED   ELECTROCHEMISTRY 

the  nickel  peroxide  and  nickelic  oxide  must  form  one  phase, 
such  as  a  solid  solution.  This  evolution  of  oxygen  is  the  cause 
of  the  loss  in  capacity  on  standing,  amounting  to  10  per  cent 
in  24  hours,  for  in  this  battery  the  capacity  is  determined  by 
that  of  the  positive  plates. 

The  change  in  the  potential  of  the  nickel  electrode  on  dis- 
charging is  shown  by  the  curve  in  Figure  75.  It  is  of  course 
similar  to  the  discharge  curve  of  the  whole  battery,  since  the 
capacity  is  determined  by  this  plate.  The  first  part  of  the 
curve,  concave  upwards,  is  due  to  the  discharge  of  the  solid 
solution  of  nickel  peroxide  in  nickelic  oxide,  as  is  shown  by 
the  fact  that  this  part  of  the  curve  entirely  disappears  if  the 
battery  stands  idle  for  twelve  hours  after  charging.  The  drop 
towards  the  end  of  the  discharge  of  0.55  volt  was  shown  by 
analysis  to  be  due  to  an  oxide  of  nickel  lying  between  Ni2O3 
and  NiO,  possibly  Ni3O4,  as  this  oxide  is  known  to  exist.  This 
second  constant  potential  becomes  shorter  as  the  current  density 
increases,  and  finally  disappears  altogether. 

The  charging  potential  of  the  nickel  plate  is  more  above  the 
potential  corresponding  to  nickelic  oxide  than  the  discharge 
curve  is  below.  This  is  because  the  first  action  in  charging 
is  to  produce  nickel  peroxide,  which  requires  a  potential  at 
least  equal  to  that  of  a  solid  solution  of  nickel  peroxide.  The 
nickel  peroxide  at  first  finds  a  large  amount  of  nickelous  oxide 
which  it  oxidizes  to  nickelic  oxide.  The  nickel  peroxide  there- 
fore disappears  rapidly  at  first,  and  with  a  low  current  density 
the  potential  of  the  plate  is  not  much  above  that  of  nickelic 
oxide.  Gradually,  however,  the  peroxide  becomes  more  con- 
centrated and  the  potential  rises.  The  nickel  peroxide  then 
begins  to  decompose  with  the  evolution  of  oxygen,  until  its 
rate  of  decomposition  equals  its  rate  of  formation.  Nickel 
peroxide  is  formed  also  by  the  electrolytic  oxidation  of  nickelic 
oxide,  so  that  its  formation  continues  even  after  all  of  the 
nickelous  oxide  ha?s  been  oxidized. 

The  efficiency  of  charging  the  nickel  plate  is  determined  by 
the  amount  of  oxygen  evolved.  The  curves  in  Figure  76  show 
this  efficiency  for  three  different  current  densities,  when  the 


THE    EDISON    STORAGE    BATTERY 


181 


discharge  was  stopped  before  the  second  step»was  reached.  It 
is  evident  from  these  curves  that  the  full  capacity  cannot  be 
obtained  without  a  loss  in  the  current  efficiency.  This  is  quite 
different  from  the  lead  storage  battery,  in  which  the  efficiency 
of  charging  is  nearly  100  per  cent  throughout  the  whole  charge, 
and  then  suddenly  falls  to  zero  at  the  end.  In  speaking  of  the 
current  efficiency  in  an  Edison  storage  battery,  the  capacity 
must  therefore  also  be  given. 

The  Negative  Plate.  —  The  negative  or  iron  plate  when 
charged  consists  of  finely  divided  metallic  iron  in  the  active 
state.  If  iron  is  reduced  at  a  high  temperature  by  hydrogen 


100 


40 


0.2 


0.3 


0.4  0.5  0,6 

AMPERE  HOURS 


o.r 


O.S 


to 


FIG.  76.  —  Efficiency  of  charging  the  nickel  plate 

and  then  placed  in  potassium  hydrate,  it  remains  inactive,  but 
after  electrolyzing  for  a  short  while  as  cathode  in  a  potas- 
sium hydrate  solution  it  becomes  active  and  has  considerable 
capacity.2 

The  iron  electrode  also  has  two  stages  in  its  discharge, 8  as 
seen  in  Figure  77.  The  first  consists  in  the  oxidation  of  iron 
to  ferrous  oxide.2  The  second  step  is  due  to  the  oxidation 
of  ferrous  to  ferric  iron,  due  to  the  iron  becoming  passive 
and  the  velocity  of  the  oxidation  of  metallic  iron  becoming  too 

2  F.  Foerster  and  V.  Herold,  Z.  f.  Elektroch.  16,  461,  (1910).     The  discussion 
of  the  iron  electrode  is  taken  from  this  article,  where  the  contrary  is  not  stated. 

3  M.  W.  Schoop,  Electrochem.  Ind.  2,  274,  (1904). 


182 


APPLIED   ELECTROCHEMISTRY 


slow.  The  oxidation  of  iron  to  ferrous  hydrate  is  then  replaced 
partly  or  entirely  by  the  oxidation  of  ferrous  to  ferric  iron.  If 
the  ferrous  hydrate  is  not  supplied  rapidly  enough  by  electro- 
chemical oxidation,  the  metallic  iron  is  oxidized  to  the  ferrous 
state  by  the  ferric  iron.  The  result  of  the  second  step  is,  there- 


40.6 


-0.2 


0  5  10  15  20  25  30 

AMPERE  MINUTES 

FIG.  77.  —  Potential  of  iron  electrode  on  discharge 


fore,  to  change  metallic  iron  to  the  ferric  state.  In  a  2.85 
normal  solution  of  potassium  hydrate  the  potential  of  the  first 
process  is  +  0.60  volt  referred  to  the  dropping  electrode  as 
zero,  the  positive  sign  referring  to  the  charge  on  the  solution 
surrounding  the  electrode.  The  potential  difference  between 
the  ferro-hydroxide  electrode  arid  a  2.85  normal  potassium 
hydrate  solution  is  +  0.47  volt.  This  difference  in  voltage 
between  the  two  steps  for  the  iron  electrode  is  therefore  only  0.13 
volt,  while  in  the  case  of  the  nickel  electrode  it  is  0.55 
volt.  This  second  step  is  of  no  practical  importance,  for  the 
iron  plate  would  not  reach  it  when  its  capacity  is  greater  than 
the  nickel. 

The  effect  of  the  addition  of  mercury  to  the  iron  plate  is 
to  increase  its  capacity  by  keeping  the  iron  in  the  active  state. 
The  beneficial  effect  of  mercury  was  discovered  by  Edison 
empirically,  but  just  how  it  keeps  the  iron  active  is  not  yet 
understood.  The  mercury  makes  it  possible,  however,  for  the 
plate  to  have  a  constant  capacity  for  the  first  step,  independent 


THE   EDISON   STORAGE    BATTERY  183 

of  the  current  density,  and  is  therefore  of  great  practical  impor- 
tance. It  has  no  effect  on  charging.  The  reason  for  making 
the  capacity  of  the  iron  plate  greater  than  that  of  the  nickel  is 
that  the  iron  electrode  should  never  be  discharged  as  far  as  the 
second  step,  for  ferric  iron  cannot  be  completely  reduced  again, 
and  the  plates  lose  in  capacity.  It  has  an  equally  bad  effect 
to  allow  the  iron  plate  to  stand  unused  in  potassium  hydrate 
exposed  to  the  air  or  to  allow  it  to  stand  in  the  air  when  moist. 
In  charging,  hydrogen  is  liberated  on  the  iron  plate  from  the 
start,  so  that  the  iron  plate  causes  a  greater  loss  in  current  than 
the  nickel,  on  which  no  gas  is  liberated  during  the  first  part  of 
the  charge.  It  was  shown  above  that  the  nickel  plate  changes 
from  Ni2O3  -1.2  H2O  to  Ni(OH)2  on  discharging,  and  the  iron 
plate  from  iron  to  ferrous  hydrate.  These  changes  may  be  rep- 
resented by  the  equations :  4 

Ni203  •  1.2  H20  +  1.8  H20  ;£  2  Ni(OH)2  +  2  OH-  +  2  F    (3) 
and  Fe  +  20H-^>Fe(OH)2-2F.  (4) 

The  sum  of  these  equations  is 

Fe  +  Ni2O3  - 1.2  H2O  +  1.8  H2O  ^±  2  Ni(OH)2 

+  Fe(OH)2+.  (5) 

This  equation  represents  the  final  result  in  the  whole  cell  on 
discharge,  when  taken  from  left  to  right,  and  on  charge,  wrhen 
taken  from  right  to  left.  These  equations  are  not  reversible  in 
the  ordinary  sense,  however,  for  they  do  not  show  that  hydrogen 
and  oxygen  are  evolved  on  charging  or  that  the  nickelous 
hydrate  is  first  oxidized  to  nickel  peroxide.  The  Edison  cell  is 
therefore  not  strictly  reversible,  and  the  equations,  though 
written  as  reversible,  are  to  be  taken  only  as  referring  to  the  initial 
and  final  states  of  the  cell.  It  is  also  to  be  noticed  that  in  adding 
the  two  equations  for  the  iron  and  the  nickel  plates  the  two 
quantities  of  electricity,  2  F,  cancel  out.  This  means  the  two 
quantities  neutralize  each  other,  thereby  producing  the  current. 
The  Electrolyte.  —  From  the  equation  (5)  it  is  evident  that 
water  is  taken  up  from  the  electrolyte  on  discharging  by  the 
plates  and  is  given  up  again  on  charging.  This  can  be  seen  by 
*  Foerster,  Z.  f.  Elektroch.  14,  285,  (1908). 


184  APPLIED   ELECTROCHEMISTRY 

the  change  in  level  in  the  solution  on  charging  and  discharging. 
According  to  equation  (5),  0.9  mole  of  water  would  be  com- 
bined or  set  free  to  one  faraday  of  electricity  passing  through 
the  cell.  Other  experiments  made  for  the  purpose  of  deter- 
mining this  quantity  gave  an  average  of  1.45  moles  of  water. 
This  agreement  is  not  all  that  could  be  desired.  There  is  no 
question,  however,  that  water  is  removed  from  the  solution  on 
discharging,  and  it  therefore  follows  that  the  electromotive 
force  of  the  battery  will  decrease  with  the  increasing  concentra- 
tion of  the  electrolyte.  This  is  verified  by  the  measurements 
of  the  following  table  : 4 


NORMALITY  OF  HYDRATE  SOLUTION 

E.  M.  F.  OF  CELL 

1.0 

1.3510 

1.15 

1.3368 

2.82 

1.3377 

5.3 

1.3349 

From  what  has  preceded,  it  will  be  evident  that  the  current 
efficiency  and  capacity  depend  on  each  other.  If  the  battery 
is  not  fully  charged,  the  current  efficiency  will  be  high,  but  the 
full  capacity  is  not  obtained.  This  can  be  obtained  only  by 
charging  after  gas  evolution  has  begun,  which  reduces  the 
current  efficiency.  When  the  cell  was  charged  and  discharged 
at  the  normal  rate  of  4  hours,  the  ampere  hour  efficiency  was 
about  75  per  cent,  and  the  voltage  efficiency  about  70  per  cent, 
making  the  energy  efficiency  about  50  per  cent.6 

5  Kennelly  and  Whiting,  Trans.  Am.  Electrochem.  Soc.  6,  146,  (1904). 


CHAPTER   XI 
THE  ELECTRIC  FURNACE 
1.    GENERAL  DISCUSSION 

THE  electric  furnace  industries  are  at  present  in  a  state  of 
rapid  development.  This  is  due  partly  to  the  manufacture  of 
a  large  number  of  new  products  made  possible  by  the  high 
temperature  attainable  in  the  electric  furnace,  and  partly  to 
improved  methods  in  the  manufacture  of  products  previously 
obtained  by  other  methods. 

The  electric  furnace  was  probably  first  used  on  a  commercial 
scale  by  the  Cowles  Brothers  in  1884  in  their  manufacture  of 
aluminum  alloys,  but  the  rapid  increase  in  its  use  began  about 
1893  with  the  production  of  calcium  carbide,  carborundum,  and 
aluminum. 

In  the  manufacture  of  many  electric  furnace  products,  heat 
at  a  high  temperature  is  the  form  of  energy  that  brings  about 
the  change  desired.  The  question  naturally  arises,  how  is  it 
possible  that  it  should  be  economical  to  obtain  heat  from  such 
an  expensive  form  of  energy  as  electricity.  There  are  several 
reasons  why  it  is  economical.  In  the  first  place,  the  temper- 
ature required  for  the  formation  of  many  electric  furnace  prod- 
ucts is  above  that  attainable  by  any  commercial  fuel.  In  such 
cases  it  is  evident  that  if  the  product  is  to  be  formed  at  all,  it 
must  be  formed  in  an  electric  furnace.  On  the  other  hand,  it 
has  been  found  economical  to  use  heat  generated  from  electricity 
in  cases  where  fuel  was  formerly  used.  This  is  due  to  a  simplifi- 
cation in  the  apparatus  and  a  saving  of  time  and  labor.  While 
electric  heat  costs  more  per  unit,  it  may  be  possible  to  reduce 
the  time  during  which  it  has  to  be  applied  to  such  an  extent 

185 


186  APPLIED    ELECTROCHEMISTRY 

that  the  quantity  of  heat  required  is  so  much  less  than  when 
fuel  is  used  that  it  more  than  saves  the  extra  cost  per  unit. 
This  is  often  the  case  on  account  of  the  fact  that  electric  heat 
is  generated  inside  the  furnace  or  container  just  where  it  is 
wanted,  while  in  the  use  of  fuel  the  heat  is  generated  outside 
the  furnace  and  has  to  penetrate  the  walls  before  reaching  the 
material  to  be  heated.  It  is  evident  that  more  heat  will  be  lost 
in  the  latter  than  in  the  former  process. 

In  those  furnaces  in  which  the  electricity  flows  through  a 
core  especially  made  for  the  purpose  and  not  through  the 
charge  itself,  the  temperature  to  which  the  core  is  raised  is  one 
of  the  factors  that  determines  the  time  required  to  bring  the 
charge  up  to  the  desired  temperature,  since  the  flow  of  heat 
between  two  bodies  is  proportional  to  their  difference  in  tem- 
perature. 

Furnaces  may  be  divided  into  three  classes :  arc  furnaces, 
resistance  furnaces,  and  induction  furnaces.  In  the  first,  as  the 
name  indicates,  the  source  of  heat  is  an  arc.  A  solid  body  to 
be  heated  is  placed  near  the  arc  and  is  heated  by  radiation. 
By  adjusting  this  distance  the  temperature  to  which  it  is  raised 
may  be  regulated.  In  case  a  gas  is  to  be  heated,  the  passage  of 
the  arc  through  the  gas  itself  brings  about  the  desired  result. 
In  the  resistance  furnaces  the  current  generates  heat  by  passing 
some  suitable  resistor.  It  is  evident  that  arc  furnaces  are  simply 
resistance  furnaces  where  the  resistor  is  a  gas;  but  nevertheless 
this  distinction  is  a  convenient  one.  Resistance  furnaces  may 
be  of  two  kinds,  first,  those  in  which  the  current  passes  through 
the  charge  to  be  treated  and  develops  heat  in  consequence  of  the 
resistance  of  the  charge,  and  second,  those  in  which  the  current 
passes  a  resistor  surrounded  by  the  charge.  The  latter  furnace 
is  used  in  those  cases  where  the  charge  itself  does  not  conduct 
well.  The  first  class  of  resistance  furnace  may  be  divided  into 
two  classes,  in  which  (1)  the  thermal  effect  is  alone  active,  and 
(2)  in  which  electrolysis  also  takes  place. 

The  induction  furnace  is  the  latest  type,  and  is  used  in  the 
steel  industry.  The  metal  to  be  heated  forms  the  secondary 
winding  of  a  transformer,  and  forms  a  closed  ring  in  an  annular 


THE    ELECTRIC    FURNACE  187 

crucible.     A   current   is   induced  from  the  primary  winding 
sufficiently  great  to  melt  the  metal. 

The  following  table  summarizes  this  classification. 

ELECTRIC  FURNACES 

1.  2.  3. 

Arc  Resistance  Induction 


1.   The  charge  con-  2.    Current  conducted 

ducts  the  current.  by  a  special  resistor. 


1.   Withelec-  2.   Without  elec- 

trolysis, trolysis. 

2.   ELECTRIC  FURNACE  DESIGN 

In  spite  of  the  fact  that  the  heat  is  generated  inside  the  furnace, 
there  is  always  some  heat  lost  by  conduction  through  the  walls 
of  the  furnace,  through  the  electrodes,  and  in  some  cases  by 
hot  gases.  To  increase  the  economy  of  furnaces  these  losses 
must  be  made  as  small  as  possible.  The  case  when  the  loss  is 
due  to  gases  requires  no  special  consideration,  but  it  will  be 
desirable  to  consider  the  losses  through  the  walls  and  the 
electrodes. 

If  H  equals  the  number. of  calories  conducted  in  one  second 
through  a  wall  of  cross  section  S,  thickness  I,  and  specific  con- 
ductivity &,  when  the  difference  in  temperature  of  the  two 
faces  is  T  and  no  heat  is  lost  through  the  ends  of  the  walls, 

rr       SkT 

then  H-— — 

l 

In  the  case  of  a  furnace,  the  cross  section  of  the  wall  is  not 
constant,  but  increases  from  the  inner  to  the  outer  surface. 
Generally  in  making  this  calculation  the  average  cross  section 
is  taken.  Where  the  walls  are  thin,  this  is  fairly  accurate,  but 
with  thick  walls  a  very  great  error  may  be  introduced.1 

1  Carl  Hering,  Trans.  Am.  Electrochem.  Soc.  14,  215,  (1908).  The  discussion 
in  the  text  is  taken  from  this  article. 


188  APPLIED   ELECTROCHEMISTRY 

For  a  complete  sphere,  inner  surface  s,  outer  surface  S,  and 
thickness  of  wall  I,  the  heat  conducted  per  second  for  unit  dif- 
ference of  temperature  is  2 


TT_ 


where  D  is  the  outside  and  d  the  inside  diameter.     For  a  cube 

6  TcDd 


I          I 

where  D  is  the  length  of  the  outer  edge  and  d  that  of  the  inner 
edge.  For  a  cylindrical  shell  of  length  (7,  thickness  of  wall  Z, 
outside  diameter  2>,  and  inside  diameter  c?, 


2-3  log" 


2  The  derivations  of  this  and  the  following  formulae,  not  given  by  Bering  in 
the  article  referred  to,  are  very  simple.  The  resistance  of  a  spherical  shell  of 
thickness  dx,  where  the  radius  of  the  shell  is  x,  is 

dE  =          ,  if  r  —  specific  resistance. 

4  7TX2 

Integrating  between  the  limits  x  =  ai  and  x  —  «2,  where  a\  and  «2  are  the  inner 
and  outer  radii  respectively, 

T-J  T     f  Ct2  — 

~T^\~a^L 

But  if  8  is  the  outer  surface  and  s  the  inner,  #=4  7ra22,  s=4  IT  «i2,  and  «2  —  «i  = 
the  thickness  of  the  shell.     Substituting  these  values, 


To  get  the  formula  for  the  cylinder  of  length  O  all  that  is  necessary  is  to  integrate 
the  equation 

dE=  between  x  =  a2  and  x  =  ai, 

2  TTCX 

giving  JR^-^-  log, 2S. 

^  TTO  (Zl 

For  the  cubical  frustum 

dB  =  r**  ,  whence  7?=  -r  f  «^£A  =  -iL  =  H, 
wx2  n  V    ai«2    /      Vs^     ^-D 

where  n  is  given  by  the  equation  S= 


THE    ELECTRIC    FURNACE 


189 


The  curves  in  Figure  78  give  an  idea  of  the  error  that  would 
result  from  using  the  mean  value  of  the  cross  section  in  place 
of  the  above  formulae.  As  abscissae  are  taken  the  thickness  of 
wall  in  terms  of  the  inner  diameter  or  edge,  and  as  ordinates 
the  conductivity  for  one  degree  difference  in  temperature  and 
for  a  substance  whose  specific  conductivity  is  one.  The  dotted 


FIG.  78.  —  Heat  loss  as  function  of  thickness  of  walls 

lines  show  the  conductivity  as  given  by  the  approximate  formula, 
and  the  full  lines  show  the  true  value.  It  is  evident  that  the 
greatest  errors  occur  in  the  cases  of  the  cube  and  sphere, 
where  they  are  quite  appreciable  when  the  thickness  of  the 
wall  equals  one  half  the  diameter  or  one  half  the  inner  edge. 
In  Table  20  the  values  of  the  heat  conducted  through  the  walls 
of  the  three  typical  furnaces  are  collected,  which  are  those  given 


190 


APPLIED   ELECTROCHEMISTRY 


in  the  plot.3     The  conductivity  and  difference  in  temperature 
are  assumed  unity. 

TABLE  20 
Heat  Conductivity  of  Spherical,  Cubical,  and  Cylindrical  Furnaces 


THICKNESS 

SPHERES 

CUBES 

CYLINDERS 

CONDUCTANCE 

CONDUCT  ANCE 

CONDUCTANCE 

By  Correct 
Formula 

By  Approxi- 
mate Formula 

By  Correct 
Formula 

By  Approxi- 
mate Formula 

By  Correct 
Formula 

By  Approxi- 
mate Formula 

0.10 

37.70 

38.3 

72.0 

73.2 

34.40 

34.60 

0.15 

27.20 

28.2 

52.0 

53.8 

23.90 

24.10 

0.20 

22.00 

23.2 

42.0 

44.4 

18.70 

18.80 

0.25 

18.90 

20.4 

36.0 

39.0 

15.50 

15.70 

0.30 

16.80 

18.6 

32.0 

35.6 

13.40 

13.60' 

0.35 

15.30 

17.5 

29.1 

33.3 

11.80 

12.10 

0.40 

14.10 

16.7 

27.0 

31.8 

10.70 

11.00 

0.45 

13.30 

16.1 

25.3 

30.7 

9.79 

10.10 

0.50 

12.60 

15.7 

24.0 

30.0 

9.06 

9.43 

0.60 

11.50 

15.3 

22.0 

29.2 

7.97 

8.38 

0.70 

10.80 

15.2 

20.6 

29.0 

7.18 

7.63 

0.80 

10.20 

15.2 

19.5 

29.1 

6.58 

7.07 

0.90 

9.77 

15.4 

18.7 

29.5 

6.10 

6.63 

1.00 

9.42 

15.7 

18.0 

30.0 

5.72 

6.28 

1.50 

8.38 

17.8 

16.0 

34.0 

4.53 

5.24 

2.00 

7.85 

20.4 

15.0 

39.0 

3.90 

4.71 

3.00 

7.33 

26.2 

14.0 

50.0 

3.23 

4.19 

The  following  example  will  show  how  this  table  may  be  used 
in  the  case  of  a  furnace  of  one  of  these  types.  Let  the  inner 
diameter  of  a  spherical  furnace  be  15  inches,  the  thickness  of 
wall  9  inches ;  to  find  the  heat  conductance  if  the  wall  consists 
of  infusorial  earth  whose  specific  heat  conductivity  is  "k  =  0.001 
in  gram  calorie  cubic  inch  units,  and  if  the  difference  in  tem- 
perature between  the  inside  and  outside  face  is  700°  C.  The 

8  Hering,  I.  c.  In  the  original  table  four  and  five  places  of  significant  figures 
are  given.  Since  the  specific  conductivity  of  refractory  substances  at  high  tem- 
peratures is  not  known  to  more  than  two  places,  only  three  places  are  here 
retained. 


THE    ELECTRIC   FURNACE 


191 


thickness  in  terms  of  the  diameter  is  -=  —  =  0.6.     Opposite 

d     15 

0.6  in  the  table  the  conductance  is  11.5.  This  number  evi- 
dently must  be  multiplied  by  c?,  &,  and  700,  giving  a  loss  of  121 
grams  calorie  per  second.  On  the  other  hand,  if  the  loss  is 
given  and  the  temperature  difference  and  conductivity  are 
known,  the  corresponding  thickness  can  be  found. 

In  the  case  of  the  cylinder,  the  conductivity  calculated  is  for 
the  cylindrical  part  alone.  These  values  must  therefore  be 
multiplied  by  the  length  of  the  cylinder,  but  not  by  the  inside 
diameter,  and  the  loss  at  the  two  ends  must  be  added. 

Unfortunately  heat  conductivities  of  refractory  substances 
are  not  accurately  known  above  1000°  C.  Recently,  however, 
the  mean  conductivities  between  room  temperature  and  1000°  C. 
of  a  number  of  refractory  substances  have  been  determined  un- 
der the  direction  of  Le  Chatelier  by  Wologdine.  The  results  4 
have  been  collected  by  Queneau  in  Table  21.  Data  are  also 

TABLE  21 
Conductivity  of  Refractory  Materials 


MATERIAL 

CONDUCTIVITY 

Gram  Calorie  per  Cm.  Cube 
per  1°  C.  Diflf.  in  Temp. 

Relative  Conductivity  in  Per 
Cent  of  Value  for  Graphite 

0.0250 
0.0231 
0.0071 
0.0057 
0.0042 
0.0039 
0.0038 
0.0035 
0.0033 
0.0027 
0.0023 
0.0020 
0.0018 

100.0 
92.0 

28.0 
23.0 
17.0 
16.0 
15.0 
14.0 
13.0 
12.0 
9.3 
7.8 
7.1 

Carborundum  brick  .... 

Fire  brick     

Checker  brick   

Silica  brick                 .... 

Infusorial  earth  brick    .     .     . 

Electrochem.  and  Met.  Ind.  7,  383,  (1909). 


192  APPLIED   ELECTROCHEMISTRY 

given  in  the  same  article  on  the  porosity  and  gas  permeability 
of  these  materials. 

The  principal  refractory  substances  for  electric  furnaces  are" 
carbon,  carborundum,  and  siloxicon.5  The  use  of  siloxicon  is 
limited  to  temperatures  below  that  at  which  it  is  converted 
into  carborundum,  and  of  carborundum  to  temperatures  below 
which  it  breaks  up  into  silicon  and  graphite.  These  sub- 
stances all  have  a  higher  thermal  conductivity  than  the  other 
less  refractory  materials,  as  seen  in  the  above  table,  and  for 
this  reason  it  is  usual  to  build  furnace  walls  in  sections,  with 
highly  refractory  material  inside,  where  the  temperature  is 
highest,  and  with  material  offering  a  high  resistance  to  the 
passage  of  heat  outside.  Carborundum,  for  instance,  is  one 
of  the  most  refractory  materials,  but  as  seen  from  the  table 
its  conductivity  is  high.  It  would,  therefore,  be  well  to  use 
this  as  a  lining  of  such  a  thickness  that  the  temperature  on  the 
outside  of  the  lining  would  not  be  too  high  for  some  material 
with  a  lower  heat  conductivity,  such  as  fire  brick  or  infusorial 
earth.  Knowing  the  dimensions,  the  total  loss  in  power,  and 
the  conductivity,  the  temperature  of  the  cool  side  of  the  lining 
is  easily  calculated.6 

The  loss  of  heat  due  to  conductance  through  the  electrodes 
will  next  be  considered.  This  loss  is  made  up  of  two  quanti- 
ties, the  heat  generated  in  the  electrode  by  the  passage  of  the 
current  and  the  heat  which  would  flow  from  the  hot  to  the  cold 
end  if  the  temperature  at  the  hot  end  were  maintained  without 
passing  a  current  through  the  electrode.  The  following  dem- 
onstration 7  will  show  how  the  total  heat  loss  due  to  the  elec- 
trodes is  related  to  these  two  losses,  and  how  electrodes  should 
be  proportioned  to  make  this  loss  a  minimum. 

In  Figure  79,  let  ab  be  a  conductor  of  heat  and  electricity 
imbedded,  except  at  its  ends,  in  a  perfect  insulator  of  heat  and 
electricity.  Let  the  temperature  at  a  be  T°  C.  and  at  6,  0°  C. 

5  FitzGerald,  Electrochem.  and  Met.  Ind.  2,  349,  (1904). 

6  For  examples  see  Hering,  Electrochem.  and  Met.  Ind.  7,  11,  (1909). 

7  Hering,  Trans.  Am.  Electrochem.  Soc.  16,  287,  (1909)  ;  also  Electrochem. 
and  Met.  Ind.  7,  442,  (1909). 


a 


THE   ELECTRIC    FURNACE  193 

Let  a  current  also  ^  JH 

pass    through    the        ^— K?TT*T»"T!T^f?.T^  ;  * 

electrode.     The  ^ 

problem  is  to  find 

the     quantity     of  FlQ  79 

heat    flowing    out 

the  cold  end,  when  a  steady  state  has  been  reached. 

Let  X  —  total  energy  in  watts  pressing  out  of  the  cold  end. 

x  =  energy  passing  any  cross  section  at  distance  I  from  the 

hot  end. 
H=  number  of  watts  that  would  flow  from  the  hot  to  the 

cold  end  were  there  no  current. 
h  —  number  of  watts  entering  the  hot  end. 
W=  number   of   watts   generated   by   the   current   in  the 

electrode. 

W 

w  =  —  where  L  =  total  length  of  electrode. 
L 

T=  total  fall  in  temperature  from  hot  to  cold  end,  when 

cold  end  is  at  0°. 

t  =  temperature  at  any  length  I  from  hot  end. 
L  =  total  length  in  centimeters. 
I  =  any  distance  from  hot  end. 
S  =  cross  section  in  square  centimeters. 
k  =  mean  heat  conductivity  for  the  given  range  of  temper- 
ature in  gram-calorie  centimeter  centigrade  degree 
units. 
r  =  mean  electrical  resistivity  for  the  given  range  in  ohms 

for  a  cube  of  one  centimeter  edge. 
1=  current  in  amperes. 
R  =  total  resistance. 

j  is  the  factor  4.19  by  which  a  given  number  of  calories 
per  second  is  multiplied  to  change  to  watts. 

Let  dl  be  an  infinitely  short  section  at  distance  I  from  the 
hot  end,  and  let  the  heat  flowing  into  this  section  be  x.  The 
heat  generated  in  the  section  by  the  current  will  be 

wdl=dx.  (1) 


194  APPLIED   ELECTROCHEMISTRY 


Also  »».-/feS  (2) 

dl 

where  •  —  is  the  heat  gradient  at  I. 
dl 

Differentiating  this  gives 

dl,  (3) 


and  eliminating  dx  between  equations  (3)  and  (1) 

d?t=        w_  Pr 

dl*         jkS         JkS* 

Since  r  and  k  are  functions  of  £,  to  be  strictly  accurate  these 
quantities  should  be  expressed  as  such  before  integrating.  For 
the  sake  of  simplicity,  however,  mean  values  for  r  and  k  for  the 
temperature  interval  considered  are  taken,  and  these  quantities 
in  equation  (4)  are  treated  as  constants.  Integrating  once 
under  this  assumption  gives 


dt  Wl 

TJ  =  a  ~~  "v"?  ' 
dl  jkS 


and  a  second  time 


In  this  equation  a  and  b  are  determined  by  the  fact  that  when 
Z  =  0,  t=T,  and  when  l=^t  =  Q. 

Substituting  these  values  in  (6)  gives 


Substituting  this  value  of  a  in  (5)  and  the  value  of  —  thus  ob- 

dl 

tained  in  (2)  gives 


This  equation  states  that  the  energy  passing  any  given  cross 
section  is  equal  to  the  energy  that  would  pass  were  no  current 
flowing,  minus  one  half  the  PR  energy,  plus  the  PR  energy 
generated  in  the  hot  end.  When  L  =  l,  since  wL  =  W, 


THE    ELECTRIC    FURNACE  195 


This  states  that  the  energy  passing  out  the  cold  end  as  heat 
equals  the  energy  that  would  pass  out  when  no  current  is  flow- 
ing, plus  one  half  the  I^R  energy. 


W 

Suppose  that  in  (7)  I  =  0,  then  x  —  h  and  h  =  If  --  -  .      In 

order   that   no   heat   shall   enter  the  hot  end,  h  =  0,   whence 

W 

ff=  —  .     The  last  equation  states  that  if  no  heat  enters  the  hot 

2 

end  from  the  furnace,  the  heat  flowing  from  the  hot  to  the  cold 
end  of  the  electrode  if  there  were  no  current  equals  ^  I*R. 

Now  the  product  of  H  x  —  -  =•?  —  -  —  ,  which  is  independent  of  S 

2  2 

and  L.     When  the  product  of  two  variables  is  a  constant,  their 
sum  is  a  minimum  when  the  two  variables  are  equal;  that  is,  in 

TTT  -prr 

the  equation  JT=  H-\  --  ,  X  will  be  a  minimum  when  H=  -—•> 

2  2 

or  the  minimum  loss  =  I^R.     Substituting  the  values  of  H  and 

TF 

W  in  H  =  —  ,  we  have  the  equation 

2 


Solving  this  for  — 
L 

y  =  0.346jfy-^-,  (9) 

and  substituting  this  value  in  the  equation  (8), 


If,  in  place  of  using  mean  values  of  the  specific  heat  conductiv- 
ity and  electrical  specific  resistance,  the  variable  values  8 

kt  =  &0(1  +  at) 

and  rt  =  r0(l  +  a^) 

are  substituted  in  the  formulse  above,  the  following  results  are 
obtained : 

8  H.  C.  Richards,  Trans.  Am.  Electrochem.  Soc.  16,  304,  (1909). 


196 


APPLIED   ELECTROCHEMISTRY 


=  0.346 


5  a\  ~  3  a 

12 


T\ 

/ 


and 


The  errors  introduced  by  using  mean  values  of  k  and  r  and 
treating  them  as  constants  will  be  small  unless  the  temperature 
coefficients  are  enormous. 

As  was  shown  above,  the  minimum  loss  of  one  electrode  is 
J?R  or  le.     Substituting  this  in  (10), 

e  =  2.89V&r2r.  0-1) 

This  voltage  is  seen  to  be  dependent  only  on  the  thermal  con- 
ductivity, electrical  re- 
sistivity, and  tempera- 
ture difference  of  the 
ends  of  the  electrodes, 
which  means  that  for 
every  material  there  is 
a  characteristic  mini- 
mum drop  of  potential 
in  the  electrodes  for 
one  degree  difference 
in  temperature  below 
*  which  it  is  not  possible 
to  go  without  increas- 
ing the  loss.  This 
minimum  drop  in 

potential  has  been  called  the  electrode  voltage. 

The  temperature  distribution  in  the  electrode  is  given  by  the 

equation : 

t^T-^^^L-.-^—  n^ 

T         *      Ct    .'7_*»  Ct     '1.  O' 


FIG.  80 


obtained  from  equation  (6)  by  substituting  in  the  values  of  a 
and  b.  The  variables  being  t  and  Z,  the  curve  is  evidently  a 
parabola.  If  no  current  flows,  w  =  0  and  the  equation  becomes 
the  straight  line  ceb  in  Figure  80. 


THE    ELECTRIC    FURNACE  197 

Making  T=Q  gives  t  =       o"Vy     '  ^e  Parabola  p.     To  find 
the  temperature  distribution  for  minimum  loss,  solve  for  T  in 

'§. 


O  -TTT 

the  equation  JKT—  =  —  ,  and  substitute  in  (12),  obtaining 


the  parabola  P.     When  —  -  is  greater  or  less  than  H,  the  tem- 

perature distribution  is  given  by  Pf  or  P"  respectively. 

In  any  problem  involving  the  design  of  electrodes,  the  tem- 
perature difference  between  the  hot  and  cold  ends  of  the  elec- 
trode and  the  kilowatts  to  be  absorbed  in  the  furnace  will  be 
given.  From  the  value  of  the  power  the  voltage  would  then 
be  made  as  high  and  the  current  as  low  as  practicable.  From 
formula  (9)  compute  the  proportion  of  the  section  to  the 
length.  The  length,  which  should  be  as  short  as  possible, 
will  be  determined  by  the  thickness  of  the  walls  of  the  fur- 
nace. Having  fixed  the  length,  the  section  is  then  obtained 
from  the  ratio  of  the  section  to  the  length.  The  two  remain- 
ing factors  which  must  be  known  are  the  values  of  the  heat 
and  electrical  conductivities  of  carbon  and  graphite,  the  only 
two  substances  used  for  electrodes  in  resistance  furnaces. 
These  values  have  not  yet  been  determined  accurately  for  high 
temperatures,  but  the  mean  values  have  been  determined  by 
Bering  between  100°  C.  and  900°  C.9  The  method  of  deter- 
mining heat  conductivity  depends  on  the  demonstration  above. 

If  in  equation  (13)  Z=0,  then  t=  ^and  k= 


In  order  to  measure  &,  a  conducting  rod  of  length  L  and  sec- 
tion S,  embedded  in  a  nonconducting  material,  is  heated  by  a 
measured  amount  of  electrical  energy  and  the  temperature  T 
measured  at  the  center.  In  order  to  have  no  heat  pass  out  the 
sides  of  the  rod,  it  is  surrounded  by  a  number  of  similar  rods 
at  the  same  temperature  as  the  one  measured.  The  electrical 
conductivity  is  obtained  from  the  ammeter  and  voltmeter  read- 
9  Trans.  Am.  Electrochem.  Soc.  16,  317,  and  315,  (1909). 


198 


APPLIED   ELECTROCHEMISTRY 


ings  and  the  dimensions.  The  values  in  Table  22  have  been 
obtained  by  this  method.9  The  units  are  centimeters,  gram 
calories,  and  ohms,  and  centigrade  degrees. 


TABLE  22 


GKAPHITE 

CARBON 

BETWEEN  100°  C.  AND 

TEMPERATURE  GIVEN 

Heat 

Electrical 

Heat 

Electrical 

Conductivity 

Kesistivity 

Conductivity 

Eesistivity 

900° 

0.291 

0.000820 

0.129 

0.00276 

390° 

0.339 

0.000838 





360° 





0.0890 

0.00422 

The  accuracy  of  these  figures  is  estimated  at  a  few  per  cent. 
The  electrode  voltage  (equation  (11))  from  these  data  for  one 
degree  for  graphite  is  0.0447  and  for  carbon  is  0.0639,  which 
means  that  the  minimum  loss  for  carbon  is  about  50  per  cent 
greater  than  for  graphite.  Later  measurements  by  Hering10 
gave  results  from  which  the  following  Table  23  has  been  com- 
puted. The  values  of  heat  conductivity  and  for  electrical 
resistivity  are  for  centimeter  cubes. 

TABLE  23 


TEMPERATURE,  C.° 

Hot  End 

Cold.  End 

Carbon 

300 

40 

0.0891 

0.00422 

701 

50 

0.124 

0.00381 

902 

60 

0.130 

0.00377 

Graphite 

355 

66 

0.339 

0.000837 

516 

70 

0.325 

0.000827 

707 

87 

0.309 

0.000802 

10  Trans.  Am.  Electrochem.  Soc.  17,  166,  (1910). 


THE    ELECTRIC    FURNACE 


199 


The  following  data  were  obtained  by  Hansen.11     The  units 
are  the  same  as  in  the  table  above. 


TABLE  24 


ACHESON  GRAPHITE 

NATIONAL  CARBON  Co.'s  ELECTRODES 

TEMPERATURE 

Heat  Con- 

Electrical 

Heat  Con- 

Electrical 

ductivity 

Kesistivity 

ductivity 

Resistivity 

25 



0.00066  to 



0.00287  to 

0.00260 

0.0254 

Between 

3200  and  200 



0.00081 





2830  and  30 

0.155 







3500  and  30 



0.0155 



The  electrical  and  thermal  conductivities  of  carbon  elec- 
trodes cannot  be  determined  above  1600°,  because  on  cooling 
the  values  do  not  come  back  to  the  original  ones,  due  to  a  par- 
tial conversion  of  the  carbon  into  graphite.11 

Besides  the  loss  in  the  electrode  itself,  a  large  loss  occurs  at 
the  contact  between  the  electrode  and  the  cable,  due  to  the 
contact  resistance.  This  resistance  varies  with  the  current 
density,  and  where  brass  clamps  are  used  on  graphite  it 
amounts  to  0.0117,  0.0045,  and  0.0039  ohms  per  square  centi- 
meter for  current  densities  of  3.7,  5.6,  and  7.4  amperes  per 
square  centimeter.11 

With  the  aid  of  the  constants  above,  a  numerical  example 
may  be  given.  Let  the  capacity  of  the  furnace  be  500  kilo- 
watts, the  current  10,000  amperes,  and  the  temperature  1700°  C. 
inside  and  100°  at  the  cold  end  of  the  graphite  electrode. 
Assuming  r  =  0.000820  and  k  =  0.291,  by  formula  (10), 
X=  17.8  kilowatts  for  each  electrode.  Assuming  for  carbon, 
r  =  0.00276  and  Jc  =  0.129,  X=  21.8  kilowatts.  Of  course,  the 
cross  sections  of  the  graphite  and  carbon  electrodes  are  not 
equal  for  equal  lengths. 

11  Trans.  Am.  Electrochem.  Soc.  16,  329,  (1909). 


200  APPLIED   ELECTROCHEMISTRY 

The  discussion  so  far  has  been  for  the  case  that  the  dimen- 
sions of  the  furnace  and  the  power  to  be  applied  in  order  to 
bring  about  a  desired  result  are  known.  If  these  are  not 
known,  an  experiment  would  usually  be  made  on  a  small  scale 
in  order  to  determine  the  relation  between  the  size  of  fur- 
nace and  the  power.  There  are  two  cases  to  be  considered, 
(1)  when  there  is  a  central  core  for  carrying  the  current, 
and  (2)  when  the  charge  to  be  heated  itself  carries  the 
current. 

In  the  first  case  the  heat  has  to  be  conducted  from  the  core 
to  the  surrounding  charge.12  The  rate  of  this  flow  is  propor- 
tional to  the  difference  in  temperature  of  the  core  and  the  sur- 
rounding charge,  the  thermal  conductivity  of  the  charge,  and 
the  surface  area  of  the  core.  If  heat  is  generated  in  the  core 
at  a  given  rate,  the  temperature  to  which  it  will  rise  in  a  given 
time  will  depend  on  the  specific  heat  of  the  core  and  the  rate 
at  which  the  heat  flows  into  the  surrounding  charge.  This 
rate  of  flow  depends  on  the  area  of  the  core  and  the  conduc- 
tivity of  the  charge.  Suppose  that  to  bring  about  the  desired 
reaction  in  a  given  charge  with  a  core  of  a  given  material  ex- 
periments are  made  with  a  small  furnace  until  the  conditions 
are  found  under  which  the  desired  reaction  is  brought  about. 
This  means  that  a  definite  amount  of  heat  must  pass  per  unit 
surface  of  the  core,  which  is  a  constant  for  these  materials  and 
is  independent  of  the  dimensions.  If  the  voltage  is  E  and  the 

TFT 

current  J,  the  energy  in  watts  per  unit  surface  is  a  =  - — — — > 

2  irJrL 

when  P  is  the  radius  and  L  the  length  of  the  core.  Collecting 
the  constants  in  one  factor,  this  may  be  written  PL  =  AEI. 
If  r  is  the  specific  resistance  of  the  core,  we  also  have 

XT  T  T 

—  =  =  B .     For  any  furnace  of  any  other  dimensions 

Lv  and  Pv  the  voltage  and  current  El  and  I±  are  given  by  the 

XT  T 

equations  P^  =  AE^   and  -1=1?— 1.      From   these  equa- 

~l  •*! 

tions  we  could  solve  for  the  new  values  E±  and  Iv  if  L1  and  P1 
M  FitzGerald,  Electroc-hem.  and  Met.  Ind.  2,  342,  (1904). 


THE    ELECTRIC    FURNACE  201 

are  given.     Usually,  however,  the  power   is   given,  and   the 
proper  dimensions  L^  and  Pl  are  desired.     Solving  for  these 


quantities,  P1  = 

and  ,  A 

The  following  is  an  example  of  the  use  of  these  formulae.  It 
was  desired  to  design  a  200-kilowatt  furnace  using  a  current 
of  4000  amperes  and  50  volts.  Experiments  on  a  small  scale 
showed  that  the  right  conditions  were  obtained  with  200  am- 
peres at  100  volts  and  a  core  365  centimeters  long  and  5.1  cen- 
timeters in  radius.  From  these  values  the  proper  length  and 
radius  for  the  large  furnace  are  found  to  be  495  centimeters 
and  37.6,  respectively. 

For  the  second  case,  where  the  current  passes  through  the 
charge  itself,  it  is  simply  necessary  to  know  the  amount  of  heat 
required  to  raise  a  given  mass  to  the  desired  temperature,  that 
is,  the  number  of  watts  per  unit  mass.  If  the  specific  heat  of 
the  charge  is  known,  this  can  be  computed  ;  if  not,  an  experiment 
on  a  small  scale  with  a  given  mass  will  determine  the  energy 
required. 


CHAPTER   XII 

PRODUCTS   OF   THE   RESISTANCE  AND   ARC  FURNACE 

1.   CALCIUM  CAKBIDE 

THE  discovery  of  calcium  carbide  is  due  to  Wohler,1  who 
prepared  it  by  the  action  of  carbon  on  an  alloy  of  calcium  and 
zinc.  Even  previous  to  Wohler,  E.  Davy  had  also  produced  it 
in  an  impure  state  without  identifying  it.2  The  commercial 
importance  of  calcium  carbide,  however,  dates  from  its  redis- 
covery by  Thomas  L.  Willson,3  which  was  nearly  simultaneous 
with  that  of  Moissan  (1892). 

The  reaction  between  lime  and  carbon  by  which  calcium 
carbide  is  produced  is  the  following  : 


As  indicated,  this  is  a  reversible  reaction,  and  according  to  the 
Phase  Rule  has  one  degree  of  freedom  ;  that  is  to  say,  at  a  given 
temperature  there  is  one  definite  pressure  of  carbon  monoxide 
which  corresponds  to  equilibrium.  At  1475°  C.  this  pressure 
has  been  found  to  be  0.82  millimeter  of  mercury.4  Above 
1500°  calcium  carbide  decomposes  into  its  elements,  but  of  course 
not  as  rapidly  as  it  is  produced,  otherwise  its  manufacture 
would  be  impossible. 

When  calcium  carbide  is  formed  from  calcium  and  diamond, 
7250  calories  are  absorbed  at  room  temperature.  When  formed 
from  lime  and  carbon,  121,000  calories  are  absorbed  at  room 
temperature,  and  the  temperature  coefficient  of  the  heat  of  the 

1  Ann.  d.  Chem,  und  Pharm.  125,  120,  (1863). 

2  Lieb.  Ann.  23,  144,  (1836).    See  Abegg,  Handbuchder  anorganischen  Chem. 
2,  119.  8  Lewes,  Acetylene,  p.  24,  (1900). 

4  Thompson,  Proc.  Am.  Acad.  45,  431,  (1910)  ;  also  Met.  and  Chem.  Eng.  8, 
327,  (1910). 

202 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   203 

reaction  has  been  calculated  to  be  3.3  calories  per  degree.6  The 
fact  that  heat  is  absorbed  when  the  above  reaction  proceeds 
from  left  to  right  shows  that  the  equilibrium  pressure  of  carbon 
monoxide  increases  with  the  temperature,  and  it  can  be  calcu- 
lated that  at  about  1840°  the  pressure  equals  one  third  of  an 
atmosphere.  If  carbon  were  heated  in  the  presence  of  air  much 
above  red  heat,  all  the  oxygen  would  be  converted  to  carbon 
monoxide,  and  if  none  escaped,  its  resulting  partial  pressure 
would  be  one  third  of  an  atmosphere.  It  would  therefore  be 
necessary  to  heat  carbon  and  lime  to  a  temperature  above  1840°  C. 
before  carbide  could  be  formed.  In  actual  practice,  however, 
the  partial  pressure  of  carbon  monoxide  would  be  less  than  one 
third  of  an  atmosphere,  in  which  case  carbide  could  be  formed 
at  a  lower  temperature.  Taking  these  facts  into  consideration, 
it  does  not  seem  probable  that  2000°  C.  is  exceeded  in  actual 
practice,  for  high  temperature  would  accelerate  the  decomposi- 
tion of  the  carbide  already  formed.  This  explains  the  fact  that 
a  resistance  furnace,  in  which  the  temperature  is  lower  than  in 
the  arc,  gives  better  yields  than  an  arc  furnace.6 

Commercial  calcium  carbide  is  dark  colored  and  crystalline 
but  if  pure  it  is  colorless  and  transparent.7  It  has  a  density  at 
18°  of  2.22,  and  is  insoluble  in  all  known  solvents.  It  is  a 
powerful  reducing  agent.  If  heated  with  metallic  oxides  it 
gives,  according  to  circumstances,  an  alloy  of  the  metal  in 
question  with  calcium  or  the  metal  itself,  probably  according 
to  the  reaction.7 

3  M20  +  CaC2  =  CaO  +  3  M2  +  2  CO 
or  5  M2O  +  CaC2  =  CaO  +  5  M2  +  2  CO2. 

It  further  has  the  property  of  absorbing  nitrogen  according  to 
the  equation 

CaC2  +  N2=CaCN2+  C, 

forming  calcium  cyanamide.  This  is  an  important  method  of 
fixing  atmospheric  nitrogen,  and  will  be  referred  to  later  under 
that  heading. 

6  Thompson,  Trans.  Am.  Electrochem.  Soc.  16,  202,  (1909). 
6  Tucker,  Alexander,   and   Hudson,  Trans.  Am.  Electrochem.   Soc.  15,  411, 
(1909).  7  Abegg,  Handbuch  der  anorganischen  Chem.  2,  p.  121. 


204 


APPLIED   ELECTROCHEMISTRY 


The  principal  use  of  calcium  carbide  is  to  produce  acetylene 
for  illumination.  This  gas  is  evolved  when  the  carbide  is 
treated  with  water,  according  to  the  reaction: 


CaC 


H20 


CaO 


C2H2. 


The  first  to  produce  calcium  carbide  on  a  commercial  scale, 
as  stated  above,  was  Thomas  L.  Willson,  at  the  Willson 
Aluminum  Works  at  Spray,8  North  Carolina.  Willson  was 
attempting  to  reduce  lime  by  heating  with  carbon,  hoping  to 
get  calcium  with  which  to  try  the  reduction  of  alumina.  It  was 
by  accident  that  the  material  produced  was  found  to  react  with 
water  and  give  off  an  inflammable  gas.  Soon  after  this  discovery 
Willson's  plant  at  Spray  was  investigated  by  Houston,  Ken- 

nelly,  and  Kennicutt.9 
Two  runs  were  made  with 
the  purpose  of  determin- 
ing the  cost  of  manufac- 
turing calcium  carbide 
under  conditions  existing 
at  that  place.  There 
were  two  furnaces  built 
in  one  structure,  as  shown 
in  Figure  81,  the  walls 
and  partition  of  which 
were  brick,  while  the 
front  was  only  partly  cov- 
ered by  cast-iron  doors. 
The  floor  space  of  each 
furnace  was  3  by  2J  feet. 
The  furnaces  united  at  a 
height  of  8  feet  into  a 
single  chimney  for  carry- 
ing off  the  gases.  The 
base  of  the  furnaces  con- 


FIG.  81.— Carbide   furnace    at  Spray,  North 
Carolina 


8J.  W.  Richards,  Electrochein.  Ind.  1,  22,  (1902).  The  date  given  by 
Richards  is  1891.  This  is  evidently  too  early  ;  see  note  3. 

9  Progressive  Age,  14,  173,  (April  15,  1896).  (Published  at  280  Broadway, 
New  York  City.) 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   205 


sisted  of  a  heavy  piece  of  iron  between,  1  and  2  inches  in  thick- 
ness, 6  feet  in  length,  and  2|  feet  in 
width.  The  iron  plate  was  completely 
covered  by  two  carbon  plates  between 
6  and  8  inches  thick.  These  formed  the 
lower  electrode.  The  upper  electrode 
of  each  furnace  was  a  carbon  block  12 
by  8  inches  in  section  and  36  inches  long, 
protected  by  an  iron  casting  -fa  inch 
thick.  The  space  between  the  casting 
and  carbon  was  filled  with  a  mixture  of 
hot  pulverized  coke  and  pitch.  The 
first  run  lasted  3  hours  with  an  aver- 
age activity  supplied  to  the  furnace  of 
144  kilowatts  at  approximately  100  volts.  FlG-  82.  -  Longitudinal  ver- 

.  tical  section  of  the  first  car- 

ThlS  made  a  total  power  consumption  of      tide    furnaces   at   Niagara 

432  kilowatt  hours,  yielding  98.0  kilo-     Falls 

grams  of  79  per  cent  pure  carbide.  The  second  run  lasted  2 
hours  and  40  minutes  with  an  average 
activity  of  146.7  kilowatts,  making  the 
^  /  total  power  consumption  388.5  killowatt 
hours  and  yielding  87.5  kilograms  of  84 
per  cent  carbide.  This  is  about  0.225 
kilograms  of  carbide  per  kilowatt  hour. 
The  cost  of  producing  carbide  at  Spray, 
working  the  furnaces  365  days  a  year  and 
24  hours  a  day,  was  estimated  at  about 
$33  per  2000  pounds  of  impure  carbide. 
This  estimate,  however,  is  made  up  of 
a  large  number  of  items  that  would  be 
considerably  changed  for  other  places. 
The  largest  producer  of  carbide  in  the 

FIG.  83.  —  Transverse    ver-  United  States  is  the  Union  Carbide  Com- 

S«35£?i£;  p^y. whose  W01'ks  are  at  Niasara  Falls-' 

ara  Falls  Their  first  furnaces  were  of  the  Willson 

type,  in  which  the  lower  electrode  was  a  small  car  which  could 
be  removed,  when  filled  with  an  ingot  of  carbide,  to  make  room 


\ 


LJ 


Air 


206 


APPLIED   ELECTROCHEMISTRY 


for  another,  as  shown  in  Figures  82  and  83.  This  type  has  been 
displaced  at  Niagara  Falls  by  the  Horry  rotary  continuous  fur- 
nace, introduced  in 
1898  and  shown  in  Fig- 
ure 84. 10  It  consists 
of  an  iron  wheel  8  feet 
in  diameter  and  3  feet 
in  width,  with  an  an- 
nular-shaped space 
around  the  circumfer- 
ence in  which  the  car- 
bide is  formed.  The 
electrodes  project  ver- 
tically down  into  this 
space.  Lime  and  car- 
bon are  fed  in,  and  as 
carbide  forms,  it  is  removed  from  the  electrodes  by  the  rotation 
of  the  furnace.  Iron  plates  hold  the  carbide  in  place  while 
under  the  influence  of  the  current.  When  the  rotation  has 
carried  it  to  the  other  side  of  the  furnace,  it  has  had  time  to 
cool,  as  there  is  only  one  complete  rotation  a  day.  The  outer 
plates  are  then  removed,  and  the  carbide  is  broken  off  in  pieces 
6  to  9  inches  thick.  Each  furnace  takes  3500  amperes  at  110 
volts  and  produces  2  short  tons  of  carbide  a  day. 


FIG.  84.  —  Horry  carbide  furnace 


COUNTRY 

PRODUCT  IN 
METRIC  TONS 

38,000 

Italy      

32000 

27000 

Norway     

25000 

Switzerland   

20000 

Austro-  Hungary     

12,000 

Sweden      ....          .                             .          .          . 

12000 

9,000 

10  Lewes,  ibid.  p.  207 ;  Richards,  Electrochem.  Ind.  1,  22,  (1902)  ;  Haber,  Z.  f. 
Elektroch.  9,  834,  (1903). 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   207 

The  production  of  the  Union  Carbide  Company  from  year  to 
year  has  not  been  made  known.  The  preceding  table  shows 
the  estimated  output  of  the  world  for  1908. u 

In  1902  the  Union  Carbide  Company  sold  carbide  to  home 
consumers  at  about  $70  a  ton,  but  exported  it  for  $50  a  ton.12 
In  1907  the  price  was  still  $  70  a  ton  in  this  country. 

In  Europe 13  the  form  of  furnace  still  used  is  of  the  Willson 
type.  In  some  cases  the  ingot  is  formed  on  a  truck  that  can  be 
removed  when  full,  and  in  others  a  stationary  crucible  is  used. 
In  the  former  case  it  has  been  found  an  improvement  to  have 
two  electrodes  suspended  over  the  truck,  so  that  the  truck  is  no 
longer  in  the  electric  circuit.  In  the  case  of  fixed  crucibles  the 
capacity  has  been  increased  in  some  cases  up  to  6000  kilowatts, 
and  a  more  satisfactory  method  of  tapping  has  been  devised. 
Formerly  the  solid  carbide  formed  around  the  tap  hole  had  to 
be  broken  away,  but  the  later  method  consists  in  inserting  an 
iron  rod  connected  to  the  upper  electrode  into  the  tap  hole, 
where  an  arc  is  formed  between  the  rod  and  the  solid  carbide. 
The  iron  and  carbide  are  both  melted  by  the  arc,  and  an  opening 
is  formed  through  which  the  melted  carbide  can  flow  out. 

With  regard  to  the  power  required  for  the  production  of  car- 
'bide,  the  only  figures  of  any  practical  importance  are  not  those 
obtained  by  calculation,  but  those  obtained  in  actual  practice. 
The  original  plant  of  Willson  produced  5.4  kilos  per  kilowatt 
day  of  24  hours9  of  80  to  85  per  cent  carbide.  At  Meran  the 
yield  is  5.8  kilos  of  78  per  cent  carbide  per  kilowatt  day.14 
At  Foyers  in  Scotland  the  yield  per  kilowatt  day  of  24  hours  is 
4.2  kilos  of  87  per  cent  carbide.15  At  Odda,  Norway,  it  lies 
between  4.5  and  5.2  kilograms.16 

The  materials 17  used  in  making  carbide  are  freshly  burnt 
lime  and  carbon  in  the  form  of  anthracite  coal,  metallurgical 
coke,  or  charcoal.  Ordinary  gas  coke  has  too  many  impurities 
for  this  purpose.  Charcoal  is  used  only  where  one  of  the  other 
forms  of  carbon  cannot  be  obtained,  as  it  generally  contains 

u  Min.  Ind.  17,  100,  (1908).  12  Min.  Ind.  11,  76,  (1902). 

13  See  Conrad,  Electrochem.  and  Met.  Ind.  6,  397,  (1908). 

14  Lewes,  Acetylene,  p.  242.  16  Lewes,  I.e.  p.  262. 
is  Electrochem.  and  Met.  Ind.  7,  213,  (1909).          17  Lewes,  pp.  264-284. 


208  APPLIED   ELECTROCHEMISTRY 

considerable  traces  of  phosphates,  which  appear  in  the  acetylene 
generated  from  the  carbide  in  the  form  of  phosphureted  hydro- 
gen. The  reaction  requires  36  parts  of  carbon  to  56  of  lime. 
In  most  ingot  carbide  furnaces  100  parts  of  lime  to  70  of  car- 
bon are  used.  In  furnaces  from  which  the  carbide  is  drawn 
off  in  the  liquid  state  a  higher  proportion  of  lime  is  used  in 
order  to  lower  the  melting  point  of  the  carbide.  This,  of 
course,  has  the  result  of  making  the  carbide  less  pure. 

It  was  at  first  supposed  that  fine  grinding  of  the  materials 
was  necessary,  but  it  has  since  been  found  that  pieces  as  much 
as  one  inch  in  diameter  may  be  used.18 

2.   CARBORUNDUM 

Carborundum  is  the  trade  name  for  the  carbide  of  silicon, 
which  has  the  formula  CSi.  It  was  probably  first  produced 
by  Despretz  in  connection  with  experiments  on  refractory  ma- 
terials, 1  in  the  course  of  which  he  heated  a  carbon  rod  em- 
bedded in  sand  by  passing  an  electric  current  through  the 
rod.  He  obtained  a  very  hard  tube  of  six  times  the  diameter 
of  the  carbon  rod,  lined  on  the  inside  with  quartz  in  the  form 
of  lampblack.  It  seems  probable  that  in  this  experiment  some 
carborundum  was  formed,  though  no  mention  is  made  of  crystals. 
It  seems  more  certain  that  carborundum  crystals  were  obtained 
by  R.  Sidney  Marsden,2  by  heating  for  several  hours  silver  or  an 
alloy  of  silver  and  platinum  in  a  Berlin  porcelain  crucible  with 
amorphous  carbon  considerably  above  the  melting  point  of  silver 
and  then  cooling  slowly  for  12  to  14  hours.  On  dissolving  the 
silver  in  nitric  acid  it  yielded  from  its  interior  a  number  of 
beautiful  crystals  of  the  hexagonal  system  and  varying  in 
color  from  light  yellow  to  dark  brown,  or  even  black.  Other 
crystals  were  found  in  the  form  of  hexagonal  prisms,  but  these 
were  in  most  cases  colorless  and  transparent.  The  colored 
crystals  were  doubtless  crystallized  carborundum,  formed  from 
the  silica  glaze  on  the  crucibles  and  the  amorphous  carbon. 

18  Blount,  Practical  Electrochemistry,  p.  230,  (1901). 

1  C.  R.  89,  720,  (1849). 

2  Proc.  Royal  Soc.  of  Edinburgh,  11,  37,  (1880-1881). 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   209 

The  white  crystals  were  evidently  silica,  as  they  dissolved  when 
boiled  in  hydrofluoric  acid. 

In  1886  A.  H.  Cowles3  obtained  some  hexagonal  crystals 
from  his  furnace  on  attempting  to  melt  quartz.  This  was  an- 
alyzed and  thought  to  be  a  suboxide  of  silicon.  On  seeing  Ache- 
son's  Carborundum  at  the  Chicago  Exposition  in  1893,  Cowles 
recognized  its  similarity  with  his  so-called  suboxide  of  silicon. 
This  resulted  in  a  lawsuit  between  the  Cowles  Electric  Smelting 
and  Refining  Company  and  the  Carborundum  Company.4  Schut- 
zenberger  and  Colson  hacLsuspected  the  existence  of  a  com- 
pound of  the  formula  Si2C2  as  early  as  1881,5  and  in  1892 
Schiitzenberger 6  obtained  the  amorphous  carbide  of  silicon  by 
heating  together  silicon,  silica,  and  carbon,  and  determined  its 
composition.  Its  color  was  a  clear  green.  Finally,  Moissan 7  has 
made  crystallized  carbide  of  silicon  in  the  following  different 
ways :  1.  Carbon  was  dissolved  in  melted  silicon  between  1200° 
C.  and  1400°  C.  from  which  crystals  of  carbide  several  milli- 
meters long  were  obtained  by  dissolving  the  silicon  in  a  boiling 
mixture  of  concentrated  nitric  acid  and  hydrofluoric  acid.  2.  By 
heating  silicon  and  carbon  in  the  proportion  of  12  parts  of  carbon 
to  28  parts  of  silicon.  The  mass  of  crystals  obtained  was  easily 
purified  by  first  boiling  in  a  mixture  of  concentrated  nitric  acid 
and  hydrofluoric  acid  and  by  then  treating  with  nitric  acid  and 
potassium  chlorate.  The  crystals  were  frequently  colored  yellow, 
but  could  be  obtained  completely  transparent.  3.  By  heating  a 
mixture  of  iron,  silicon,  and  carbon  in  the  electric  furnace,  giv- 
ing a  metallic  fusion  containing  crystals  of  carbide  of  silicon. 
The  excess  of  iron  or  silicon  was  then  dissolved.  4.  By  heating 
silica  and  carbon  in  the  electric  furnace.  5.  By  the  action  of 
the  vapor  of  silicon  on  the  vapor  of  carbon.  This  experiment 
was  made  in  a  small  carbon  crucible  containing  fused  silicon. 
The  bottom  of  the  crucible  was  heated  to  "  the  highest  tempera- 

8  Proc.  of  the  Soc.  of  Arts  for  1885-1886,  p.  74,  Boston. 

4FitzGerald,  Carborundum,  in  the  Engelhardt  Mongraphien  iiber  Ange- 
wandte  Elektrochemie. 

*C.  R.  92,  1508,  (1881).  6C.  R.  113,  1089,  (1892). 

7  Moissan,  The  Electric  Furnace,  translated  by  Lehner,  p.  274,  (1904). 


210  APPLIED   ELECTROCHEMISTRY 

ture  of  the  electric  furnace."  After  the  experiment,  slightly 
colored,  very  hard  and  brittle  crystals  in  prismatic  needles  of 
carbon  silicide  were  found.  The  description  of  this  experi- 
ment is  far  from  convincing.  If  the  crystals  were  found  in  the 
silicon,  there  is  no  evidence  of  the  action  of  one  vapor  on  the 
other,  but  even  the  original  article8  does  not  state  where 
the  crystals  were  found,  which  would  be  necessary  to  decide 
the  question. 

In  1891  at  Monongahela,  Pennsylvania,  E.  G.  Acheson  9  dis- 
covered the  crystallized  carbide  of  silicon,  in  carrying  out  some 
experiments  with  the  object  of  producing  crystallized  carbon. 
The  object  was  to  dissolve  carbon  in  melted  silicate  of  alu- 
minum, or  clay,  and  by  cooling  to  cause  the  carbon  to  crystallize. 
The  first  experiments  were  carried  out  in  an  iron  bowl  lined 
with  carbon  in  which  was  placed  a  mixture  of  carbon  and  clay. 
The  mixture  was  fused  by  means  of  an  electric  current  passing 
between  the  bowl  and  a  carbon  rod  directly  over  it.  On  fusion 
a  violent  reaction  took  place,  and  after  cooling  a  few  bright 
blue  hard  crystals  were  found.  These  were  first  supposed  to 
be  carbon,  but  later  were  taken  for  a  compound  of  alumina  or 
corundum  and  carbon,  from  which  the  name  carborundum  was 
made  up.  Subsequent  to  this  it  was  found  that  better  results 
were  obtained  when  silica  was  used  in  place  of  clay,  and  when 
common  sodium  chloride  was  added.  The  reason  for  this  was 
evident  when  the  following  analysis  of  the  product  was  made: 

Silicon 62.70  per  cent 

Carbon 36.26  per  cent 

Aluminum  oxide  and  ferric  oxide     .     .     .     .     .     .  0.93  per  cent 

Magnesium  oxide 0.11  per  cent 

This  showed  the  substance  in  the  pure  state  to  be  CSi. 

The  furnace  in  which  these  experiments  were  carried  out 
was  made  of  refractory  bricks,  the  interior  dimensions  being 
10  by  4  by  4  inches.  The  current  was  carried  by  a  core  of 
granulated  carbon,  as  shown  in  Figure  85. 

8C.  R.  117,  425,  (1893). 

8  Journ.  of  the  Franklin  Inst.  136,  194  and  279,  (1893). 


PRODUCTS   OF   THE    RESISTANCE   AND   ARC   FURNACE      211 


Figure  86  shows  an  end  view  of  this  furnace  and  the  layers 
of  different  materials  after  a  run.     B  is  a  solid  mass  of  sand 


FIG.  85. — Longitudinal  section  of  Acheson's  experimental  carborundum  furnace 

and  carbon  held  together  by  fused  salt.  C  is  chief  product  of 
the  reaction,  crystallized  carbide  of  silicon.  W  represents  a 
white  or  gray-greenish-looking  shell, 
and  consists  of  small  pieces  the  size 
of  the  original  grains.  They  are 
soft,  and  may  easily  be  reduced  to 
fine  powder,  and  are  of  no  value  as 
an  abrasive,  though  analysis  shows 
them  to  be  principally  carbide  of  sili- 
con. It  is  amorphous  carborundum, 
or  carborundum  fire  sand.  G-  is 

,  .,  ,        ...  ,  ,  FIG.  86.  —  Transverse    section    of 

graphite  mixed  with    carborundum,      Aches0n's  experimental  carbo- 
and  D  is  the  core,  only   ,  portion  of      rundum  furnace 
which  becomes  graphitized  even  though  used  repeatedly.      The 
output  of  this  small  furnace  was  \  pound  a  day.10 

The  furnaces  used  at  Monongahelainl893  were  18  inches  wide, 
12  inches  deep,  and  6  feet  long.  The  core  was  of  granular 
carbon  in  the  form  of  a  sheet  10  inches  wide,  1  inch  deep,  and 
5J  feet  long.  In  7|  to  8  hours  a  portion  of  the  charge  was 
transformed  into  50  pounds  of  crystallized  carborundum. 

On  moving  to  Niagara  Falls  the  furnaces  were  construe  ted  as 
shown  in  Figure  87. n  The  end  walls  are  built  of  refractory 


10  FitzGerald,  Journ.  Franklin  Inst.  143,  81,  (1897). 

11  FitzGerald,  Carborundum,  p.  8.  . 


212 


APPLIED   ELECTROCHEMISTRY 


brick  and  clay,  and  carry  electrodes,  52,  consisting  of  rectangu- 
lar carbon  rods  clamped  together.  Contact  is  made  with  the 
copper  cables  by  the  copper  plates,  £>5,  as  shown.  A  are  the 
brick  side  walls  of  the  furnace  put  together  without  cement. 
D  is  the  mixture,  C  the  core  of  granulated  carbon,  and  c  is  fine 
carbon  powder  for  the  purpose  of  making  contact  between  the 
carbon  electrodes  and  the  core.  Up  to  1907  the  total  length  of 
this  furnace  was  7  meters  ;  the  inside  dimensions  were,  length, 
5  meters,  width,  1.8  meters,  and  height,  1.7  meters.  The  elec- 
trodes consisted  of  25  carbon  rods,  86  centimeters  in  length, 
and  10  by  10  centimeters  in  cross  section.  The  core  was  53 


FIG.  87.  —  Longitudinal  section  of  carborundum  furnace 

centimeters  in  diameter.     A  perspective  of  the  furnace  in  oper- 
ation is  shown  in  Figure  88. 

The  power  absorbed  by  each  furnace  is  746  kilowatts.  The 
voltage  varies  from  210  volts  at  the  start  to  75  volts  when  the 
resistance  of  the  core  had  dropped  to  its  final  constant  value. 
Soon  after  the  current  is  turned  on,  carbon  monoxide  is  pro- 
duced, due  to  the  oxidation  of  the  carbon  in  the  core  and  in  the 
charge.  The  gas  is  always  lighted,  and  burns  during  the  run. 
When  the  temperature  has  become  sufficiently  high,  carbo- 
rundum is  formed  according  to  the  following  reaction  : 

Si02  +  3  C  =  CSi  +  2  CO. 

The  heating  lasts  36  hours,  and  produces  3150  kilograms  of 
crystallized  carborundum,  surrounding  the  core  to  a  depth  of 


PRODUCTS   OF   THE    RESISTANCE    AND   ARC   FURNACE  213 


214  APPLIED   ELECTROCHEMISTRY 

from  25  to  30  centimeters,  This  corresponds  to  8.5  kilowatt 
hours  per  kilogram,  which  is  a  great  improvement  over  the  first 
furnaces  of  the  Carborundum  Company  at  Monongahela,  which 
were  built  for  100  kilowatts,  and  yielded  one  kilogram  of  car- 
borundum for  an  expenditure  of  17.6  kilowatt  hours.  The 
present  electrical  equipment  of  the  Carborundum  Company  at 
Niagara  Falls  has  a  capacity  of  5300  kilowatts.12 

The  raw  materials  used  by  the  Carborundum  Company  con- 
sist of  ground  quartz  99.5  percent  silica,  coke,  such  as  is  used 
in  blast  furnaces,  sawdust,  and  sodium  chloride.  The  object 
of  the  sawdust  is  to  make  the  charge  porous  to  facilitate  the 
escape  of  the  carbon  monoxide.  The  coke  used  for  the  core  is 
sifted  to  get  rid  of  the  powder;  that  used  for  the  charge  is 
powdered.  The  charge  is  made  up  in  lots  of  500  kilograms,  and 
has  the  following  composition  : 

Quartz 261  kilograms 

Coke 177  kilograms 

Sawdust 53  kilograms 

Salt 9  kilograms 

500 

In  1907  the  furnace  plant  was  remodeled,13  and  the  furnaces 
were  made  9.15  meters  long  and  3.67  meters  wide.  These  are 
presumably  outside  dimensions.  The  power  absorbed  is  now 
1600  kilowatts  with  the  maximum  current  20,000  amperes. 
The  yield  of  each  furnace  in  one  run  is  15,000  pounds,  or 
6800  kilograms,  of  crystallized  carborundum.  On  coining  from 
the  furnace  the  carborundum  is  ground,  treated  with  concen- 
trated sulphuric  acid  to  remove  harmful  impurities,  and  is  washed 
with  water.  It  is  then  sorted  into  different  sizes. 

Table  25  gives  the  production  of  carborundum  in  this  country 
and  its  value  including  the  year  1909. 14 

12  Electrochem.  and  Met.  Ind.  7,  190,  (1909). 

13  Min.  Ind.  16,  155,  (1907);  17,  112,  (1908). 
"  Min.  Ind.  18,  86,  (1909). 


PRODUCTS    OF   THE    RESISTANCE   AND   ARC   FURNACE      215 
TABLE  25 


YEAR 


METRIC  TONS 


VALUE  IN  DOLLARS 


1891  . 0.023 

1892  ..'..... 1 

1893  .'-...-. 7 

1894 24 

1895 .  102 

189G        540 

1897        564 

1898        724 

1899        791 

1900  .     . ' 1089 

1901 1742 

1902        1698 

1903 2160 

1904        3203 

1905        2539 

1906        '.     .  2824 

1907        3418 

1908        2226 

1909  2983 


366,000 
154,000 
151,000 
157,000 
168,000 
268,000 
261,000 
333,000 
494,000 
391,000 
435,000 
452,000 
294,000 
389,000 


In  1902  the  cost  of  manufacture  was  4  cents  to  5  cents  a  pound, 
and  during  this  year  the  average  selling  price  was  10  cents  a 
pound.15  The  only  producer  in  this  country  is  the  Carborundum 
Company  of  Niagara  Falls.  In  Europe  it  is  produced  at  La 
Bathie,  France,  Iserhohn,  Germany,  and  Prague.16 

Carborundum  is  used  principally  as  an  abrasive  and  as  a  sub- 
stitute for  ferrosilicon  in  the  manufacture  of  steel.  In  1902 
one  third  the  total  output  was  consumed  in  this  industry.17  The 
abrasive  qualities  of  carborundum  are  affected  by  its  great 
brittleness,  on  account  of  which  it  will  not  cut  diamond  unless 
reduced  to  a  fine  powder.9  It  is  made  into  polishing  wheels  by 
mixing  with  a  certain  amount  of  kaolin  and  feldspar  as  a  binder, 
compressing  in  a  hydraulic  press,  and  burning  in  a  furnace  such 
as  is  used  in  the  manufacture  of  porcelain.  Carborundum  is 


15  Min.  Ind.  11,  78,  (1902). 
"Min.  Ind.  11,  227,  (1902). 


"Mm.  Ind.  10,  253,  (1901). 


216 


APPLIED    ELECTROCHEMISTRY 


also  used  in  wireless  telegraphy  as  a  detector,  and  in  a  different 
form,  known  as  Silundum,1*1  us  a  resistance  for  heating  purposes. 
Silundum  is  made  by  exposing  rods  of  carbon  to  the  vapor  of 
silicon,  which  penetrates  the  carbon,  changing  it  to  silundum 
arid  thereby  increasing  its  electrical  resistance  to  a  sufficient 
extent  to  make  it  a  good  resistor.  In  the  form  of  bricks  car- 
borundum is  used  as  a  refractory  material  in  building  furnaces, 
when  the  temperature  to  be  withstood  is  very  high. 

Silicon  carbide  is  colorless  when  pure,10  but  the  commercial 
product  is  black,  due  either  to  carbon,  iron,  or  to  a"  thin  film  of 
silica19  on  the  surface.  The  following  analysis  is  due  to  Moissan  : 


PER  CKNT 


Theoretical 


Silicon 69.70  69.85  70.00 

Carbon 30.00  29.80  30.00 

The  following  is  an  analysis  of  Acheson's  product :  u 

Silicon 64.93  per  cent 

Carbon  and  oxygen 33.26  per  cent 

Loss  in  beating 1.36  per  cent 

Aluminum 0.25  per  cent 

Calcium,  magnesium,  iron  ....     trace 

99.80  per  cent 

When  the  same  material  was  purified  by  hydrochloric  acid  and 
sodium  hydrate,  by  heating  in  oxygen,  and  finally  by  heating 
with  hydrofluoric  acid,  its  analysis  gave  the  following  result : 

Silicon 69.10  per  cent 

Carbon 30.20  per  cent 

A12O3  and  Fe2O3 0.49  per  cent 

CaO 0.15  per  cent 

99.94  per  cent 

The  density  is  3.2.  The  crystals  have  been  found  by  Frazier 
to  be  rhombohedral.20  It  easily  scratches  ruby,  and,  as  stated 
above,  when  finely  powdered,  will  polish  diamond. 

re  Boiling,  Electrochem.  and  Met.  Ind.  7,  25,  (1909). 

w  Min.  Ind.  16,  155,  (1907).  20  Journ.  Franklin  Inst.  136,  289,  (1893). 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   217 

When  carborundum  is  heated  to  a  sufficiently  high  tempera- 
ture silicon  is  vaporized,  leaving  carbon  in  the  form  of  graphite. 
The  temperature  at  which  decomposition  takes  place  has  been 
found  by  Tucker  and  Lampen21  to  be  2220°  and  the  temperature 
of  formation,  1950°C.  There  is  hardly  a  doubt  that  both  the 
reactions, 

SiO2  +  3  C  =  SiC  +  2  CO 

and  SiC  =  Si  +  C 

are  reversible.  The  temperature  of  formation  therefore  depends 
on  the  partialpressure  of  carbon  monoxide,  and  the  temperature 
of  decomposition  on  the  partial  pressure  of  silicon  vapor,  for 
according  to  the  Phase  Rule  each  of  these  systems  has  one 
degree  of  freedom.  These  values,  however,  probably  represent 
fairly  well  the  temperatures  of  formation  and  decomposition  in 
the  Acheson  furnace. 

Carborundum  is  not  attacked  by  sulphur  or  oxygen  at 
1000° C.,7  but  according  to  Acheson  it  is  oxidized  in  an  at- 
mosphere containing  considerable  oxygen  at  1470°  C.22  It  is 
attacked  slightly  by  chlorine  at  600°.  Fused  potassium  nitrate 
and  chlorate,  boiling  sulphuric  and  hydrofluoric  acids  are  all 
without  action.  The  same  is  true  of  a  boiling  mixture  of  con- 
centrated nitric  and  hydrofluoric  acids.  On  the  other  hand  it 
is  attacked  by  fused  potassium  hydrate,  forming  potassium 
carbonate  and  silicate. 

3.     SlLOXICON1 

There  are  a  number  of  compounds,  besides  the  carbide  of 
silicon,  that  contain  carbon  and  silicon  in  the  same  proportions 
as  the  carbide.  In  1881  Schiitzenberger  and  Colson  2  prepared 
a  compound  of  the  formula  SiCO  by  heating  silicon  in  an  at- 
mosphere of  carbon  dioxide.  The  reaction  is  stated  to  be 

3  Si  +  2  CO2  =  SiO2  +  2  SiCO. 

21  Journ.  Am.  Chem.  Soc.  28,  853,  (1906). 

22  Electrochem.  Ind.  i,  373,  (1903). 

1  The  name  given  by  Acheson  to  compounds  of  carbon,  silicon,  and  oxygen  in 
varying  amounts.  2  C.  R.  92,  1508,  (1881). 


218  APPLIED   ELECTROCHEMISTRY 

The  same  compound  was  formed  at  a  higher  temperature  by 
the  direct  union  of  silicon  and  carbon  monoxide.  A  compound 
of  the  formula  Si404N  was  formed  in  a  similar  way.  On  heat- 
ing silicon  in  a  stream  of  hydrogen  saturated  with  benzene  at 
50°  to  60°  C.  two  compounds  were  obtained,  one  of  the 
formula  C2Si,  and  the  other  of  a  variable  composition,  but  fre- 
quently containing  more  oxygen  than  corresponds  to  the 
formula  CSiO2.3  On  heating  silicon  in  a  vapor  of  carbon  sul- 
phide two  compounds  deposited  in  the  cold  part  of  the  com- 
bustion tube  corresponding  to  the  formulae  SiSO  and  SiS.  In 
the  boat  containing  the  silicon  a  greenish  powder  was  obtained 
which,  when  purified  by  boiling  in  potassium  hydrate  and  treat- 
ing with  hydrofluoric  acid,  had  the  composition  Si4C4S.  This 
when  heated  in  a  current  of  oxygen  gave  Si4C4O2.  These 
bodies  all  look  alike  and  can  be  distinguished  only  by  analysis.4 
They  are  pale  green  powders,  infusible,  unattackable  by  hydro- 
fluoric acid  or  strong  solutions  of  caustic  alkali.  Fused  caus- 
tic alkali  decomposes  them,  giving  alkali  silicate  and  carbonate. 
They  resist  oxidation  at  red  heat.  It  will  be  seen  that  these 
compounds  also  resemble  the  compound  obtained  by  Schiitzen- 
berger4  in  1892,  and  which  analysis  showed  to  be  SiC,  though 
the  color  of  the  latter  compound  is  described  as  a  clear  green. 
It,  therefore,  seems  that  carborundum  exists  in  two  forms,  one 
crystalline  and  the  other  amorphous,  while  the  amorphous  form 
has  all  the  appearance  of  other  compounds  containing  silicon 
and  oxygen  in  the  same  proportions  as  carborundum,  together 
with  a  variable  amount  of  oxygen.  From  the  contradictory 
statements  6  found  in  the  literature  it  seems  that  the  layer  of 
material  which  is  formed  just  outside  the  carborundum  consists 
of  silicon,  carbon,  and  oxygen  in  varying  amounts,  and  that  it 
goes  by  the  names  of  amorphous  carborundum,  carborundum 

8  Colson,  C.  R.  94,  1316,  1526,  (1882). 

4  Schiitzenberger,  C.  R.  114,  1089,  (1892). 

6  In  Min.  Ind.  15,  93,  (1906),  it  is  stated  that  another  product  of  the  carborun- 
dum furnace  is  amorphous  carborundum  or  carborundum  fire  sand,  and  that 
siloxicon  is  a  second  product  obtained  when  insufficient  coke  is  present,  consist- 
ing of  carbon,  silicon,  and  oxygen,  while  on  p.  96  the  statement  is  made  that 
amorphous  carborundum  contains  carbon,  silicon,  and  oxygen. 


PRODUCTS   OF   THE    RESISTANCE    AND   ARC   FURNACE      219 

fire  sand,  or  siloxicon.  The  latter  name  is  due  to  Acheson, 
who  took  out  a  patent  for  its  production  in  1903. 6 

In  the  manufacture  of  siloxicon  it  is  important  not  to  have 
sufficient  carbon  in  the  charge  to  reduce  the  silica  completely, 
and  to  keep  the  temperature  constant  within  certain  narrow 
limits.  For  this  purpose  the  furnace  is  built  with  more  than 
one  core,  thus  making  the  distribution  of  temperature  more 
even.  The  charge,  consisting  of  one  third  carbon  and  two 
thirds  silica,  is  made  up  of  powdered  carbon,  powdered  silica, 
and  sawdust,  the  silica  and  carbon  contents  of  the  sawdust 
being  taken  into  account. 

The  density  of  siloxicon  is  2.7.7  When  heated  in  an  atmos- 
phere containing  a  large  amount  of  oxygen  to  about  1470°  C., 
it  is  oxidized,  giving  silica  and  carbon  dioxide,8  while  in  the 
absence  of  oxygen  at  a  higher  temperature  it  is  converted  into 
carborundum. 

Siloxicon  is  used  to  make  crucibles  and  for  furnace  lining,  as 
it  is  not  attacked  by  melted  metals  or  by  slags. 

4.    SILICON 

The  manufacture  of  silicon  is  now  carried  out  by  the  Carbo- 
rundum Company  according  to  patents  of  F.  J.  Tone.1 

Arc  furnaces  are  used  in  which  two  vertical  electrodes  ex- 
tend for  a  considerable  depth  into  the  charge  of  coke  and  sand. 
The  furnace  is  built  of  fire  brick  lined  inside  with  carbon.  Each 
furnace  has  a  capacity  of  910  kilowatts,  and  the  metal  is  tapped 
out  at  intervals  of  a  few  hours  in  ingots  weighing  from  600  to 
800  pounds.  It  is  made  in  different  grades,  varying  from  90  to 
97  per  cent  pure.  Silicon  is  used  principally  in  the  steel  in- 
dustry in  place  of  ferrosilicon.  The  production  of  silicon  in 
1908  was  600  long  tons,  valued  at  $72,000.2  Previous  to  its 

•  Electrochem.  and  Met.  Ind.  1,  287,  (1903). 

7  FitzGerald,  Electrochem.  and  Met.  Ind.  2,  439,  (1904). 

e  Acheson,  Electrochem.  and  Met.  Ind.  2,  373,  (1904). 

1  Electrochem.  and  Met.  Ind.  7,  192,  (1909). 

2  Min.  Ind.  17,  13,  (1908). 


220  APPLIED    ELECTROCHEMISTRY 

manufacture  by  the  Carborundum  Company  the  price  of  silicon 
was  $4  a  pound. 

Silicon  can  also  be  made  in  small  laboratory  furnaces.3 

5.    GRAPHITE 

Graphite  was  known  to  the  ancients,  but  up  to  the  time  of 
Scheele  no  distinction  was  made  between  it  and  the  closely  similar 
substance  molybdenum  sulphide,  MoSg.1  Both  leave  a  mark  on 
paper  and  were  called  plumbago  on  account  of  the  belief  that 
they  contained  lead. 

In  order  to  define  graphite  more  definitely,  Berthelot 2  proposed 
that  only  that  variety  of  carbon  be  given  this  name  which,  on 
oxidation  with  powerful  oxidizing  agents  at  low  temperatures, 
gives  graphitic  oxide.  Graphitic  oxide  has  different  properties, 
depending  on  the  differences  in  the  graphite  from  which  it  is 
made,  but  all  varieties  are  insoluble  and  deflagrate  on  heating. 
Amorphous  carbon,  when  oxidized  with  a  mixture  of  potassium 
chlorate  and  fuming  nitric  acid,  the  oxidizing  agent  used  by 
Berthelot,  is  changed  to  a  soluble  substance,  and  diamond  is  not 
affected.  This  is  a  method  of  separating  the  three  different 
kinds  of  carbon. 

The  artificial  production  of  graphite  by  dissolving  carbon  in 
cast  iron  and  allowing  to  cool  slowly  was  first  observed  by 
Scheele  in  1778. 1  It  has  since  been  made  by  Moissan  by  dis- 
solving in  iron,  as  well  as  in  a  number  of  other  metals,  and  by 
heating  pure  sugar  carbon  in  the  electric  arc.3  Diamond  also 
may  be  changed  to  graphite  by  heating  in  the  electric  arc. 
Despretz,4  in  his  work  on  carbon,  produced  graphite  by  heating 
carbon  in  an  electric  furnace.  These  observations  do  not  agree 
with  those  of  Acheson,  who  early  in  his  experience  in  the  manu- 
facture of  carborundum  noticed  that  graphite  occasionally  formed 

8  Tucker,  Met.  and  Chem.  Eng.  8,  19,  (1910). 

1  Roscoe  and  Schorlemmer,  Treatise  on  Chemistry,  3d  ed.  Vol.  1,  p.  730. 

2  Ann.  de  Chim.  et  de  Phys.  (4)  19,  393,  (1870). 

3  Moissan,    The   Electric  Furnace,  p.  61.      See  also  FitzGerald,  Kunstlicher 
Graphite,  Vol.  15  of  the  Engelhardt  Monographien. 

*  C.  R.  28,  755  ;  281,  48  and  709,  (1849). 


PRODUCTS    OF   THE    RESISTANCE    AND   ARC    FURNACE       221 

next  to  the  core, 5  and  that  when  coke  from  bituminous  coal  was 
used  for  the  core  quite  a  large  amount  of  it  was  converted  into 
graphite,  whereas  when  the  purer  petroleum  coke  was  used  very 
little  was  so  changed.  The  greater  the  amount  of  impurity  in 
the  coke,  the  larger  was  the  amount  of  graphite  produced.  These 
facts  led  Acheson  to  the  theory  that  graphite  is  not  produced 
by  simply  heating  carbon,  but  that  a  carbide  must  first  be  pro- 
duced and  then  decomposed  by  a  higher  temperature,  volatilizing 
the  metallic  element  and  leaving  the  carbon  in  the  form  of 
graphite.  The  effect  of  the  impurities  is  catalytic,  since  the 
amount  of  graphite  formed  was  always  too  great  to  be  accounted 
for  by  the  simple  decomposition  of  the  quantity  of  carbide  cor- 
responding to  the  impurity  present.  If  only  a  small  amount  of 
impurity  is  present,  it  is  lost  by  volatilization  before  all  the  carbon 
can  be  graph itized.  Acheson  also  found  that  the  production  of 
graphite  was  greatly  increased  by  adding  a  considerable  quantity 
of  any  substance  that  could  form  a  carbide,  such  as  silica,  alumi- 
num oxide,  lime,  or  iron  oxide.6  At  first  the  charge  was  made  up 
with  enough  impurity  to  change  all  the  carbon  to  carbide  at 
once.  For  example,  a  charge  would  consist  of  50  per  cent  coke, 
with  sand,  salt,  and  sawdust.  Carborundum  was  then  formed 
and  by  heating  to  a  higher  temperature  the  carborundum  is 
decomposed,  leaving  graphite.  It  was  found,  however,  that  so 
much  carbide-forming  element  was  not  necessary  and  that  such 
substances  as  anthracite  coal  that  had  impurities  evenly  dis- 
tributed through  them  could  be  converted  into  very  pure  graph- 
ite.7 This  is  at  present  one  of  the  principal  kinds  of  carbon  used 
in  this  industry. 

Intimate  mixture  of  carbon  and  the  impurity  is  not  necessary, 
as  the  carbide-forming  element  can  be  vaporized  and  caused  to 
penetrate  the  entire  charge,  thereby  converting  it  to  graphite.8 
Petroleum  coke  is  one  form  of  carbon  used  in  this  process. 
Lumps  of  the  coke  are  imbedded  in  powder  formed  from  the 
same  material  and  5  per  cent  of  iron  oxide  is  sprinkled  in.  The 
iron  oxide  is  reduced,  iron  is  formed  at  the  bottom  of  the  furnace, 

5  Journ.  Franklin  lust.  147,  476,  (1899).  7  U.  S.  Pat.  645,285,  (1899). 

6  U.  S.  Pat.  568,323,  (1893).  »  U.  S.  Pat.  711,011,  (1900). 


222 


APPLIED    ELECTROCHEMISTRY 


and  as  the  temperature  is  raised  volatilizes  and  penetrates  the 
whole  charge.  A  very  soft  quality  of  graphite  is  obtained  when 
the  carbide-forming  material  is  more  than  20  per  cent  by  weight 
of  the  charge,  but  less  than  the  amount  necessary  to  change  all 
the  carbon  to  carbide  at  once.9 

The  furnaces  for  graphitizing  carbon  in  bulk  have  a  central 
core  similar  to  the  carborundum  furnace.10 


FIG.  89.  —  Section  of  graphite  furnace  for  rectangular  electrodes 


FIG.  90.  —  Section  of  graphite  furnace  for  circular  electrodes 

In  making  graphite  into  electrodes,  crucibles,  or  other  finished 
products,  a  mixture  of  97  per  cent  carbon  and  3  per  cent  iron 

9  U.  S.  Pat.  836,355,  (1906).        10  Richards,  Electrochein.  Ind.  1,  54,  (1902). 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   223 

oxide11  is  mixed  with  a  binding  material  consisting  of  water  and 
a  little  molasses,  and  is  molded  into  the  desired  form.  The 
molded  objects  are  then  dried  and  placed  in  the  furnace,  where 
they  are  changed  to  graphite  without  altering  their  shape.  Fig- 
ures 89  and  90  show  the  methods  of  arranging  rectangular  and 


FIG.  91. — Electric    furnace    in   which    graphite   is  made  artificially  by  the 
International  Acheson  Graphite  Company,  Niagara  Falls 

circular  electrodes  respectively.  The  base  of  the  furnace  consists 
of  bricks,  covered  with  a  refractory  material,  h.  The  end  walls, 
6,  are  of  brick  and  hold  the  carbon  electrodes,  c.  The  bottom 
of  the  furnace  is  covered  with  a  layer  of  granulated  coke  about 
5  centimeters  thick,  on  which  the  electrodes  are  placed  in  piles 
at  right  angles  to  the  axis  of  the  furnace,  separated  from  each 
other  by  about  one  fifth  the  width  of  the  electrodes.  This  space 
is  then  filled  .with  granulated  coke,  g,  arid  the  furnace  is  covered 
with  a  mixture  of  coke  and  sand,  i.  Figure  91  is  from  a  photo- 
graph of  the  furnace  now  used  for  graphitizing  carbon  in  all 
forms. 

u  U.  S.  Pat.  617,029,  (1898). 


224 


APPLIED    ELECTROCHEMISTRY 


The  following  data  are  given  by  FitzGerald :  12 

Distance  between  terminals 360  inches 

Length  of  space  filled  by  electrodes 302  inches 

Length  of  space  filled  by  granular  carbon   ....         58  inches 

Length  of  electrodes  under  treatment 24  inches 

Width  of  electrodes  under  treatment 5  inches 

Height  of  pile  of  electrodes 17  inches 

Initial  voltage       210  volts 

Initial  amperage 1400  amperes 

Final  voltage 80  volts 

Final  amperage 9000  amperes 

In  1902  the  plant  of  the  International  Acheson  Graphite 
Company  consisted  of  ten  furnaces  and  1000  available  horse 
power.  In  1909  the  plant  was  increased  to  22  furnaces  and  4000 
horse  power.13 

The  yearly  production  of  manufactured  graphite  is  given  in 
Table  26.14  " 


TABLE  26 
The  Production  of  Graphite 


YEAR 

POUNDS 

VALUE  IN  DOLLARS 

1897  

162,000 

10,100 

1898  

186,000 

11,600 

1899  

406,000 

32,500 

1900    .  .  

861,000 

68,900 

1901        

2,500,000 

119,000 

1902  .  .  .  

2,359,000 

111,000 

1903  

2,620,000 

179,000 

1904  

3,248,000 

218,000 

1905    

4,596,000 

314,000 

1906  

4,868,000 

313,000 

1907  

6,924,000 

484,000 

1908  

7,386,000 

503,000 

1909          .  . 

6,871,000 

467,000 

12  Electrochem.  and  Met.  Ind.  3,  417,  (1905). 

13  Electrochem.  and  Met.  Ind.  7,  187,  (1909). 

i*  Min.  Ind.  18,  384,  (1909).     The  figures  in  the  table  are  rounded  off. 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   225 


6.    CARBON  BISULPHIDE 

Great  improvement  has  been  made  in  the  manufacture  of 
carbon  bisulphide  by  using  an  electric  furnace  in  place  of  the 
small  clay  or  iron  retorts 
which  have  to  be  heated  ex- 
ternally. In  the  old  process, 
only  a  small  fraction  of  the 
heat  applied  to  the  outside  of 
the  retort  penetrated  to  the 
mixture  of  carbon  and  sulphur 
inside,  and  the  process  was 
so  disagreeable  on  account  of 
small  leaks  and  the  high  tem- 
peratures of  the  retort  room 
that  some  manufacturers  gave 
it  up  altogether.  E.  R.  Tay- 
lor,1 however,  has  succeeded  in 
overcoming  these  difficulties 
entirely  by  the  use  of  the  fur- 
nace shown  in  cross  section  in 
Figure  92,  patented  in  18992 
and  in  operation  at  Perm  Yan, 
New  York.  This  furnace  is 
12.5  meters  high  and  the  diam- 
eter at  the  base  4.87  meters.3 
At  a  height  of  3.68  meters  the 
diameter  is  reduced  to  2.5  me- 
ters for  a  distance  of  4.87  me- 
ters, where  it  narrows  down  to 
the  top  for  the  remaining 
length.  The  electrodes  are  at 
the  base  and  are  four  in  num- 
ber, arranged  90  degrees  apart.  FIG.  92.— Taylor's  electric  furnace  for 
Opposite  electrodes  are  Con-  making  carbon  bisulphide 

1  E.  R.  Taylor,  Trans.  Am.  Electrochem.  Soc.  1, 115,  (1902)  and  2, 185,  (1902) 

2  U.  S.  Pat.  688,364,  filed  1899,  renewed  1901. 

3  Haber,  f.  Elektroch.  9,  399,  (1903). 

Q 


226  APPLIED    ELECTROCHEMISTRY 

nected  to  the  same  terminal  of  the  alternating  current  machine. 
Wear  on  the  electrodes  is  reduced  to  practically  nothing  by 
covering  them  with  conducting  carbon,  which  acts  as  the  re- 
sistor. Charcoal  is  fed  in  at  the  top  and  sulphur  through  the 
annular  spaces  in  the  walls,  thus  preventing  loss  of  heat.  The 
sulphur  is  melted  by  the  heat  which  would  otherwise  be  lost 
through  the  walls,  and  flows  down  on  to  the  electrodes,  where 
it  is  heated  to  a  temperature  at  which  it  combines  with  carbon. 
The  carbon  bisulphide  vaporizes,  passes  off  through  the  top  of 
the  furnace,  and  is  condensed  in  cooling  coils.  The  furnace  is 
so  tight  that  no  odor  is  noticeable,  and  its  operation  is  contin- 
uous. The  production  in  1903  was  3175  kilograms  per  day,  with 
a  consumption  of  220  horse  power  3  and  the  furnace  had  been  in 
operation  for  two  and  a  half  years  with  only  one  interruption 
for  the  purpose  of  cleaning  out. 

7.   PHOSPHORUS 

Phosphorus  is  another  product  the  manufacture  of  which 
has  been  improved  by  the  use  of  heat  derived  from  electricity. 
The  older  method  consists  in  treating  calcium  phosphate  with 
sulphuric  acid,  which  changes  the  triphosphate  to  monophos- 
phate  : 

Ca3(P04)2  +  2  H2S04  =  2  CaSO4  +  CaH4(PO4)2. 

The  monophosphate  is  then  mixed  with  carbon  and  dried,  by 
which  it  is  changed  to  metaphosphate  : 

CaH4(P04)2  =  Ca(P08)2  +  2  H2O. 

The  metaphosphate  is  then  heated  in  small  retorts  in  which 
the  following  reaction  takes  place  : 

3  Ca(PO3)2  +  10  C  =  Ca3(PO4)2  +  10  CO  +  4  P. 

This  process  is  imperfect  in  that  a  portion  of  the  phosphorus 
is  changed  in  the  last  operation  to  the  product  with  which  the 
operation  is  begun.  Wohler  proposed  the  use  of  silica  and 
carbon,  by  which  all  the  phosphorus  would  be  recovered,  as 
shown  by  the  following  reaction  : 

Ca3(PO4)2  +  3  SiO2  +  5  C  =  3  CaSiO3  +  5  CO  +  2  P, 


PRODUCTS   OF   THE    RESISTANCE    AND   ARC   FURNACE      227 


but  it  was  never  successful  till  the  introduction  of  the  electric 
furnace,  on  account  of  the  difficulty  of  obtaining  the  necessary 
temperature  and  of  finding  vessels  to  withstand  it.1  In  1889 
the  use  of  electric  furnaces  for  the  manufacture  of  phosphorus 
was  patented  by  J.  B.  Readman.2  The  process  does  not  seem 
to  have  been  immedi- 
ately employed  on  a 
large  scale,  however. 
In  189T  the  firm  of 
Allbright  and  Wilson 


built  works  at  Niagara 
Falls,  using  300  horse 
power,  for  making 

phosphorus    in    the 

fnr        The  Roadman-Parker  electric  furnace  for  produc- 


ing phosphorus 
The      furnaces  FlG.  93.  —  Vertical  FIG.  94.  —  Horizontal 

are  illustrated  in  Fig-  section  section 

ures  93  and  94.     Each  produces  170  pounds  a  day. 

Over   half   the   world's   production   of    phosphorus   is   now 
made  in  electric  furnaces.4 


8.    ALUNDUM 

Fused  aluminum  oxide,  chemically  identical  with  corundum, 
has  received  the  trade  name  of  Alundum.  The  process  for 
making  this  abrasive  in  the  electric  furnace  was  patented  in 
1900  by  C.  B.  Jacobs.6  His  furnace  was  rectangular  in  shape, 
made  of  sheet  iron  and  brick,  and  was  lined  inside  with  car- 
bon. An  arc  was  formed  between  four  pairs  of  electrodes  near 
the  movable  bottom  of  the  furnace.  As  the  aluminum  oxide 
fused  and  covered  the  bottom  of  the  furnace,  it  was  gradually 
lowered,  thereby  making  a  layer  of  fused  aluminum  oxide 
which  cooled  slowly.  This  process  gives  the  abrasive  a  hard- 
ness greater  than  corundum. 

i  Min.  Ind.  14,  494,  (1905).  »Min.  Ind.  6,  637,  (1897),  7,  557,  (1898). 

2U.  S.  Pat.  147,943,  (1889).  *Min.  Ind.  9,  768,  (1900). 

6U.  S.  Pat.  659,926,  (1900). 


228 


APPLIED   ELECTROCHEMISTRY 


The  Norton  Emery  Wheel  Company  of  Worcester  are  the 
sole  manufacturers  of  alundum.  Their  factory  is  at  Niagara 
Falls.  Bauxite,  the  raw  material,  is  dehydrated  before  feeding 
into  the  furnaces.  The  yearly  production  is  given  in  Table  27.6 


TABLE  27 
Production  of  Alundum 


YEAR 

POUNDS 

VALUE  IN  DOLLARS 

1904  

4  020  000 

281  400 

1905            

3  612  000 

259  840 

1906   

4,331,000 

303  190 

1907   

6,751,000 

405,090 

1908   ...  

3,160,000 

189,600 

1909   

13,758,000 

814,680 

9.    ALUMINUM 

With  the  exception  of  silicon  and  oxygen,  aluminum  is  the 
most  widely  distributed  element  in  nature,1  occurring  princi- 
pally as  silicates  in  clays.  Only  a  limited  number  of  its  com- 
pounds can  be  used  for  extracting  aluminum,  however,  chief 
among  which  is  bauxite,  A1O3H3.  The  name  aluminum  is 
derived  from  alumen,  a  term  applied  by  the  Romans  to  all 
bodies  of  astringent  taste. 

The  attempts  to  isolate  aluminum  date  from  1807,  when  Davy 
was  unsuccessful  in  applying  to  this  problem  the  method  em- 
ployed in  isolating  the  alkali  metals.  Oersted  seems  to  have 
made  aluminum  in  1824  by  heating  the  chloride  with  potassium 
amalgam.  Wohler  in  1827  obtained  aluminum  by  decompos- 
ing the  anhydrous  chloride  with  potassium,  and  in  1864  Bunsen 
and  Deville  obtained  it  independently  by  the  electrolysis  of 
fused  aluminum  chloride.  Previous  to  the  production  by  the 
method  of  electrolysis  now  used,  the  halide  salts  were  the 
source  of  the  metal  and  were  reduced  by  metallic  sodium. 

Alumina  can  be  reduced  by  carbon  to  metallic  aluminum  by 


6Min.  Ind.  18,25,  (1909). 


1  Thorpe,  Die.  of  Chem.  1,  63,  (1890). 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   229 

heating  to  a  temperature  above  2100°  C.,2  but  it  is  always  mixed 
with  aluminum  carbide,  from  which  it  can  be  removed  by 
remelting,  and  obtained  in  a  compact  form.  This  is  evidently 
not  a  method  of  making  aluminum  that  could  be  satisfactorily 
carried  out  commercially.  If,  however,  a  metal  such  as  copper 
is  added  to  the  mixture,  the  aluminum  can  be  obtained  as  an 
alloy  with  this  other  metal.  This  process  was  patented  in 
1884  by  the  Cowles  brothers.3  The  cheap  production  of  pure 
aluminum,  however,  was  made  possible  by  the  discovery  of 
C.  M.  Hall4  that  alumina,  dissolved  in  a  molten  mixture  of 
aluminum  fluoride  and  the  fluoride  of  another  metal,  forms  an 
electrolyte  which  may  be  decomposed  by  an  electric  current, 
liberating  aluminum  at  the  cathode  and  oxygen  at  the  anode. 
Hall's  original  patent  specifies  a  mixture  of  169  parts  by  weight 
of  aluminum  fluoride  and  116  parts  of  potassium  fluoride, 
corresponding  to  the  formula  K2A12F8,  and  states  that  this  may 
be  made  more  fusible  by  replacing  part  of  the  potassium 
fluoride  by  lithium  fluoride,  or  by  simply  adding  the  latter  to 
the  above  mixture.  Another  receipt  is  84  parts  of  sodium 
fluoride  to  169  of  aluminum  fluoride,  which  may  be  made  by 
adding  aluminum  fluoride  to  cryolite,  a  mineral  of  the  com- 
position A1F8  •  3  NaF.  He  placed  the  carbon-lined  crucible  in  a 
furnace,  melted  the  mixture,  added  alumina,  and  electrolyzed 
with  an  anode  of  copper  or  carbon.  Copper  is  said  to  be 
covered  with  an  oxide  which  protects  it  from  further  action. 

Subsequent  patents  show  that  these  mixtures  worked  well 
at  first,  but  became  less  efficient  after  being  electrolyzed  some 
time.  A  dark  substance  formed  which  interfered  with  the 
electrolytic  action,  increased  the  resistance,  and  necessitated  a 
change  of  the  bath.  This  Hall  attempted  to  overcome  by 
using  a  bath  of  calcium  and  aluminum  fluoride  of  the  com- 
position 2  A1F3'  CaF2.6  This  increases  the  density  to  such  an 
extent  that  the  aluminum  floats  to  the  surface.  It  evidently 

2  Hutton  and  Petavel,  Phil.  Trans.  207,  421,  (1907)  ;  Askenasy  and  Lebedeff, 
Z.  f.  Elektroch.  16,  565,  (1910). 

8  U.  S.  Pat.  319,795,  (1884).     Also  Proc.  Soc.  of  Arts,  1885-1886,  p.  74. 

*  U.  S.  Pat.  400,664  and  400,766,  filed  1886. 

•  U.  S.  Pat.  400,664,  filed  1888. 


X 
230  APPLIED   ELECTROCHEMISTRY 

was  not  satisfactory,  for  subsequently  a  bath  made  up  of  234 
parts  calcium  fluoride,  421  parts  cryolite,  845  parts  aluminum 
fluoride,  and  3  to  4  per  cent  calcium  chloride  was  patented.6 
It  was  claimed  that  the  chloride  prevented  the  clogging  of  the 
bath  even  when  in  continuous  operation.  It  is  evident  the 
dark  color  must  have  come  from  carbon,  as  no  clogging 
occurred  with  any  of  the  baths  when  a  metal  was  used  as 
cathode.7  In  this  case,  of  course,  an  alloy  of  aluminum  would 
be  obtained. 

As  carried  out  on  a  large  scale,  the  crucibles  were  never 
heated  externally,  but  simply  by  the  passage  of  the  current  it- 
self. This  double  use  of  the  current  to  keep  the  bath  melted 
and  to  electrolyze  at  the  same  time  was  patented  by  Charles  S. 
Bradley.8  In  describing  his  process,  cryolite  is  considered  the 
electrolyte.  The  two  patents  of  Hall  and  Bradley  taken  to- 
gether represent  the  process  as  actually  carried  out. 

In  1887  Paul  Heroult  patented  a  very  similar  process  for 
producing  aluminum  alloys.9  This  process  consisted  in  fusing 
pure  alumina  and  keeping  it  in  the  fused  state  by  the  current, 
which  at  the  same  time  decomposes  the  oxide  electrolytically. 
The  cathode  is  a  melted  metal,  with  which  the  aluminum  is  to 
be  alloyed,  and  the  anode  is  carbon.  Serious  objections  were 
found  to  using  any  flux.  Among  those  tried  and  discarded  was 
cryolite.  The  patent  states  that  satisfactory  results  were  ob- 
tained with  a  carbon  crucible  20  centimeters  in  depth  and  14 
centimeters  in  diameter  at  the  top,  a  carbon  anode  5  centimeters 
in  diameter,  and  a  current  of  400  amperes  at  from  20  to  25  volts. 
This  voltage  is  four  or  five  times  that  specified  by  Hall.  Brad- 
ley's  patent  for  the  simultaneous  use  of  the  current  for  electrol- 
ysis and  heating  was  therefore  earlier  than  Heroult's,  and  as  it 
is  stated  in  Heroult's  patent  that  he  had  failed  to  get  good  re- 
sults when  any  flux  was  mixed  with  the  aluminum  oxide,  there 
is  no  question  of  priority  over  Hall's  patents.  It  does  not  seem, 
therefore,  that  the  statement  often  met  with,  that  the  processes 

s  U.  S.  Pat.  400,666,  filed  1888.  7  U.  S.  Pat.  400,667,  filed  1888. 

8  U.  S.  Pat.  464,933,  filed  1883,  granted  1891. 
•  U.  S.  Pat.  387,876,  filed  December,  1887. 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   231 


of  Hall  and  Heroult  are  identical,  is  borne  out  by  the  patents.10 
The  Hall  patents  for  the  composition  of  the  bath  expired  in 
1905  and  the  Bradley  patents  in  1909. u 

The  only  producer  of  aluminum  in  this  country  is  the  Alumi- 
num Company  of  America,  previous  to  1907  known  as  the  Pitts- 
burg  Reduction  Company.12  This  company  controls  three  plants, 
situated  at  Niagara  Falls,  Massena,  New  York,  and  Shawinegan 
Falls,  Canada.  These  plants  were  enlarged  in  capacity  in  1907 
to  40,000  horse  power,  20,000  horse  power,  and  15,000  horse 
power  respectively.13  The  six  European  companies  producing 
aluminum  show  a  maximum  consumption  of  97,500  horse  power.13 
The  furnaces  used  by  the  American  company  consist  of  cast 
iron  troughs  lined  with  carbon.14  The  anode  is  composed  of  48 
carbon  rods  3  inches  in  diameter  and  15  inches  long,  manufac- 
tured by  the  aluminum  company  for  its  own  use.12  Each  fur- 
nace takes  about  10,000  amperes  at  about  5.5  volts.  The  yield 
is  1.75  pounds  of  aluminum  per  horse  power  day.1*  The  metal 
sinks  to  the  bottom  and  is  drawn  off,  while  alumina  is  thrown 
in  as  it  is  used  up.  The  temperature  of  the  bath  may  be  in- 
ferred from  the  following  melting  points  of  mixtures  of  cryolite 
and  alumina.16 

TABLE  28 
Melting  Points  of  Mixtures  of  Cryolite  and  Alumina 


PEE  CENT 
CRYOLITE 

M.  P.,  DEGREES 
CENTIGRADE 

PER  CENT 
CRYOLITE 

M.  P.,  DEGREES 
CENTIGRADE 

100 

1000 

92 

992 

97 

974 

90 

980 

96 

960 

85 

994 

95 

915 

80 

1015 

94 

960 

93 

982 

10  See  for  example  Pring,  Some  Electrochemical  Centres,  p.  26  (1908). 
"  Min.  Ind.  17,  23,  (1908).  18  Min.  Ind.  6,  11, 15,  (1907). 

12  Min.  Ind.  15,  11,  (1906).  u  Min.  Ind.  14,  15,  (1905). 

is  Pyne,  Trans.  Am.  Electrochem.  Soc.  10,  163,  (1906). 


232 


APPLIED   ELECTROCHEMISTRY 


The  production  of  aluminum  in  the  United  States  and  Canada 
is  given  in  Table  29. 16 

TABLE  29 
Production  of  Aluminum  in  the  United  States  and  Canada 


YEAR 

POUNDS 

VALUE  IN 
DOLLARS 

VALUE  PER  POUND 
IN  DOLLARS 

1897    

4,000,000 

1,400,000 

0.35 

1898    

5,200,000 

1,690,000 

0.33 

1899              

6,500,000 

2,113,000 

0.33 

1900    

7,150,000 

2,289,000 

0.32 

1901    ....... 

7,150,000 

2,238,000 

0.31 

1902    

7,300,000 

2,285,000 

0.31 

1903                        .     .     . 

7,500,000 

2,325,000 

0.31 

1904    

7,700,000 

2,233,000 

0.29 

1905    

11,350,000 

3,632,000 

0.32 

1906    

14,350,000 

5,166,000 

0.36 

1907              ..... 

26,000,000 

10,920,000 

0.42 

1908 

13  000  000 

4,095,000 

0.32 

1909    

15,000,000 

3,345,000 

0.22 

The  total  production  of  the  world  for  1909  is  estimated  at 
24,200  metric  tons,  or  53,300,000  pounds.  The  cost  of  manu- 
facture excluding  amortization  is  said  to  be  about  15  cents  a 
pound.16 

On  reading  a  description  of  the  different  expedients  patented 
by  Hall  to  prevent  the  baths  from  clogging,  becoming  discolored, 
and  ceasing  to  operate  properly,  it  is  not  surprising  that  diffi- 
culties are  encountered  on  attempting  to  use  the  reduction  of 
aluminum  as  a  laboratory  experiment.  Haber  and  Geipert17 
succeeded  in  a  few  runs,  though  in  the  last  run  they  met  with 
irregularities.  The  immediate  difficulty  that  stops  an  experi- 
ment on  a  small  scale  is  a  polarization  at  the  anode,  due  to  a 
thin  film  of  gas,18  which  reduces  the  current  to  such  a  point  that 
the  bath  freezes  up.  If  a  higher  voltage  is  applied  it  heats  the 

is  Min.  Ind.  18,  17,  (1909). 
IT  Z.  f.  Elektroch.,  8,  1,  and  26,  (1902). 

i8  Thompson,  Electrochem.  and  Met.  Ind.  7,  19,  (1909).  Also  Neumann  and 
Olsen,  Met.  and  Chem.  Eng.  8,  185,  (1910). 


PKODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   233 

bath  too  much  locally  and  burns  up  the  aluminum.  By  the 
use  of  an  anode  with  a  large  area  this  can  be  prevented  to  a 
certain  extent.18 

One  of  the  principal  uses  for  aluminum  is  in  the  iron  and 
steel  industry  as  a  reducing  agent.19  As  is  well  known,  it  has 
replaced  copper,  tin,  and  brass  to  a  great  extent  in  the  manu- 
facture of  a  large  number  of  objects  in  which  lightness  is 
desired. 

10.   SODIUM  AND  POTASSIUM 

Sodium  and  potassium  were  first  isolated  by  Davy l  by  electro- 
lyzing  the  corresponding  fused  hydrates.  In  this  process 
sodium  is  liberated  at  the  cathode  while  the  negatively  charged 
hydroxyl  ion  is  liberated  at  the  anode.  Two  of  these  ions  when 
discharged  react  together  according  to  the  reaction: 

2  OH  =  H2O  +  O. 

A  certain  amount  of  metallic  sodium  dissolves  in  the  hy  irate, 
diffuses  to  the  anode,  and  coming  in  contact  with  the  water 
reacts  to  form  hydrate  with  the  liberation  of  hydrogen.2  It  is 
therefore  possible  to  have  both  hydrogen  and  oxygen  evolved 
at  the  anode,  resulting  in  explosions.  At  the  same  time  sodium 
peroxide  (Na2O2)  is  formed.  The  water  formed  at  the  anode  is 
not  driven  off  by  the  temperature  of  the  bath  ;  on  the  contrary 
it  has  been  found  that  very  moist  air  is  dried  to  a  certain  extent 
in  passing  through  the  melted  hydrate.2 

The  apparatus  nearly  universally  used  for  the  production  of 
sodium  and  potassium  is  due  to  Hamilton  Young  Castner3  and  is 
shown  in  Figure  95.  It  consists  in  a  cast-iron  box  with  an  iron 
cathode,  H,  insulated  from  the  box  and  held  in  an  iron  pipe 
fastened  into  the  bottom  of  the  cell.  The  space  between  the 
pipe  and  electrode  is  filled  with  melted  hydrate  which  is  allowed 
to  solidify  before  the  electrolysis  is  begun.  Surrounding  the 

19  For  a  detailed  account  of  the  various  purposes  to  which  aluminum  is  applied, 
see  A.  E.  Hunt,  Journ.  Franklin  Inst.,  Vol.  144,  (1897). 

1  Phil.  Trans.,  1808,  pp.  5  and  21. 

2  Lorenz,  Elektrolyse  Geschmolzener  Salze,  I,  25,  (1905). 
8  U.  S.  Pat.  452,030,  filed  1890. 


234 


APPLIED   ELECTROCHEMISTRY 


cathode  is  a  fine  iron  gauze  diaphragm,  M,  outside  of  which  is 
the  iron  anode,  F.  The  metal  is  liberated  on  the  cathode  and 
floats  to  the  surface  of  the  hydrate,  where  it  collects  in  an  iron 
cylinder  forming  a  continuation  of  the  diaphragm.  It  is  re- 
moved by  an  iron  spoon  with  fine  perforations,  which  allow  the 
hydrate  to  drain  off,  but  which  holds  the  metal.  The  hydrate 
is  added  as  it  is  used  up,  and  the  process  is  continuous.  An 
important  point  is  to  maintain  the  temperature  as  low  as  pos- 
sible, not  over  20°  above  the  melting  point  of  the  hydrate.  The 


FIG.  95.  —  Castner's  cell  for  producing  sodium  and  potassium 

higher  the  temperature  the  less  the  yield  in  metal,  due  of  course 
to  its  greater  solubility  in  the  melted  hydrate.  As  the  temper- 
ature increases,  the  yield  becomes  less,  until  it  finally  reaches 
zero.  At  best  the  current  efficiency  is  said  to  be  only  about  45 
per  cent.4  In  the  patent  gas  heating  is  provided,  though  it  is 
stated  that  the  current  can  be  so  regulated  as  to  keep  the  proper 
temperature  without  external  heating. 

There  are  other  processes  very  similar  to  that  of  Castner, 
some  of  which  are  in  use,6  which  will  be  omitted  as  presenting 

4  Ashcroft,  Trans.  Am.  Electrochem.  Soc.  9,  123,  (1906). 

6  See  H.  Becker,  Die  Elektrometallurgie  der  Alkalimetalle,  p.  52,  (1903). 


PRODUCTS    OF   THE    RESISTANCE    AND   ARC    FURNACE      235 


no  new  principles;  but  the  principle  of  the  following  process, 
due  to  Ashcroft,4  will  be  described  because  of  its  novelty  and 
in  spite  of  the  fact  that  it  does  not  seem  as  yet  to  have  been 
carried  out  on  a  commercial  scale.  Melted  sodium  chloride  is 
electrolyzed  with  a  lead  cathode.  The  lead  sodium  alloy  formed 
is  let  into  another  cell  containing  melted  sodium  hydrate.  Here 
the  lead  alloy  acts  as  the  anode  and  forms  sodium  hydrate  with 
the  hydroxyl  ions  liberated  on  its  surface,  thus  avoiding  the 
formation  of  water  and  oxygen.  At  the  cathode  sodium  is  lib- 
erated and  removed.  To  decompose  the  chloride  7  volts  are 
required,  and  2  volts  for  the  hydrate  when  this  anode  is  used. 
The  voltage  is  therefore  about  twice  that  required  in  the 
Castner  cell;  but  as  the  current  efficiency  is  about  90  per  cent, 
or  twice  that  in  the  Castner  process,  the  yield  per  unit  of 
power  is  the  same  in  the  two  cases.  The  advantages  claimed 
by  Ashcroft  are  shown  in  the  following  table: 


ASHCKOFT  PROCESS 

CASTNER  PROCESS 

0.5  cent 

5  cents 

Cost  of  power  per  pound  of  sodium  .     . 

per  pound 
1  to  5  cents 
1  cent 

per  pound 
1  to  5  cents 
2£  cents 

Upkeep  and  standing  charges    .... 

2.5  cents 

2  cents 

Total  

5  to  9  cents 

10  to  14  cents 

per  pound 

per  pound 

The  saving  comes  in  the  greater  cheapness  of  the  raw  material, 
and  there  would  be  a  further  saving  in  the  value  of  the  chlorine 
produced. 

The  world's  production  of  sodium  in  1907  is  estimated  at  from 
3500  to  5000  tons.6  In  the  United  States  there  are  two  com- 
panies producing  about  2000  tons  a  year.  The  Electrochem- 
ical Company  at  Niagara  Falls  uses  the  Castner  process,  while 
the  Virginia  Electrolytic  Company  at  Holcomb  Rock,  Virginia, 
is  said  to  employ  a  process  in  which  fused  sodium  chloride  is 
electrolyzed. 

e  Min.  Ind.  17,  772,  (1908). 


236  APPLIED   ELECTROCHEMISTRY 

A  large  part  of  the  sodium  made  is  consumed  in  the  manu- 
facture of  sodium  cyanide  and  sodium  peroxide.  The  process 
for  cyanide  7  consists  in  passing  ammonia  over  the  metal  heated 
in  an  iron  retort  to  300  to  400°  C.,  forming  sodamide : 

2  Na  +  2  NH3  =  2  NaNH2  +  H2. 

This  is  then  treated  with  charcoal  previously  heated  to  redness, 
giving  the  cyanide 

NaNH2  +  C  =  NaCN  +  H2. 

A  recent  purpose  to  which  the  metal  has  been  put  is  the  dry- 
ing of  transformer  oils.  Ashcrof t 4  believes  a  reduction  in  the 
price  may  increase  its  uses  materially,  such  as  making  primary 
cells,  obtaining  hydrogen  by  the  decomposition  of  water,  and 
even  for  transmitting  electric  power.  The  specific  conductiv- 
ity is  only  about  one  third  that  of  copper,8  but  if  equal  weights 
of  metal  are  considered  between  two  given  points,  the  conduc- 
tivity would  be  three  times  that  of  copper,  as  the  density  of 
copper  is  about  nine  times  that  of  sodium.  Some  experiments 
have  actually  been  carried  out  in  power  transmission  with  the 
sodium  protected  in  iron  pipes.9 

11.    CALCIUM 

Calcium  was  first  isolated  by  Davy  in  1808,  by  combining 
the  methods  previously  used  by  him  with  those  of  Berzelius 
and  Pontin.1  Lime  was  mixed  with  red  oxide  of  mercury, 
slightly  moistened  and  placed  on  a  piece  of  platinum.  A  glob- 
ule of  mercury  in  a  cavity  at  the  top  acted  as  negative  elec- 
trode, giving  on  electrolysis  an  amalgam  of  calcium,  from  which 
the  mercury  was  distilled. 

Bunsen2  obtained  calcium  in  very  small  quantities  contain- 
ing a  little  mercury  by  electrolyzing  with  a  high  current 
density  a  boiling  concentrated  solution  of  calcium  chloride 

7  Roscoe  and  Schorlemmer,  2,  276,  (1907). 

8  Landolt-Bornstein  Tables,  3d  ed. 

»  Belts,  Min.  Ind.  15,  688,  (1906)  and  El.  World,  48,  914,  (1906). 

1  Alembic  Club  Reprints,  No.  6,  p.  48,  Ostwald  Klassiker,  No.  45. 

2  Fogg.  Ann.  91,  623,  (1854),  in  an  article  on  the  preparation  of  chromium. 


PRODUCTS  OF  THE  RESISTANCE  AND  ARC  FURNACE   237 


acidified  with  hydrochloric  acid.  The  cathode  was  amalga- 
mated platinum  wire.  Rathenau3  was  first  to  obtain  calcium 
in  a  compact  form  in  fairly  large  quantities  by  a  rather  original 
method.  The  bath 
consists  of  calcium 
chloride  very  little 
above  its  melting 
point.  An  iron 
rod  is  used  as  cath- 
ode,  which  just 
touches  the  surface 
of  the  bath.  As 
the  melting  point 
of  calcium  is  a  little 
higher  than  that  of  C 
the  bath,  it  solidi- 
fies on  depositing 
and  adheres  to  the 
rod,  which  is  grad- 
ually raised,  thus 
drawing  out  a  stick 
of  calcium  with  a 
certain  amount  of 
chloride  adhering 
to  it.  The  melt- 
ing point  of  the 
electrolyte  may  be 

lowered   by   adding   FIG.  96.  —  Cell  of  Seward  and  von  Kiigelgen  for  the  pro- 

calcium       fluoride.  duction  of  calcium 

The  anode  may  be  a  carbon  crucible  in  which  the  salt  is  contained,4 
though  Rathenau  does  not  specify  his  arrangement.  The  ex- 
perience of  the  author  has  been  that  this  is  a  much  better  plan 
than  that  adopted  by  P.  Wohler,5  where  the  salt  is  held  in  an 
iron  vessel  and  a  carbon  anode  dips  into  the  bath.  Due  to  the 

8  Z.  f.  Elektroch.  10,  608,  (1904). 

*  J.  H.  Goodwin,  Proc.  Am.  Phil.  Soc.  43,  381,  (1904). 

6  Z.  f.  Elektroch.  11,  612,  (1905). 


238  APPLIED   ELECTROCHEMISTRY 

high  anode  current  density  in  this  case,  the  gas  is  more  likely 
to  stop  the  current  by  polarization.  The  heat  due  to  the  cur- 
rent is  sufficient  to  keep  the  salt  melted. 

Calcium  is  made  in  this  country  only  by  the  Virginia  Elec- 
trolytic Company  at  Holcomb  Rock,  Virginia.6  The  process 
is  supposed  to  consist 7  in  electrolyziiig  melted  calcium  chloride 
in  a  cell  patented  by  Seward  and  von  Kiigelgen,8  shown  in 
Figure  96.  This  cell  consists  of  a  circular  iron  box,  J.,  through 
the  bottom  of  which  projects  a  conical  iron  cathode,  B,  insulated 
from  the  box  by  insulating  material,  aa.  The  anode,  (7,  is  a  car- 
bon lining  also  insulated  from  the  iron  box.  Above  the  cathode 
and  concentric  with  it  is  a  water-cooled  collecting  ring,  E,  which 
separates  the  metal  rising  to  the  surface  from  the  chlorine. 
The  metal  accumulates  till  the  ring  is  full.  The  top  layer  is 
solid,  due  to  the  cooling  of  the  air,  and  the  bottom  is  soft  or 
melted.  The  solid  part  is  fastened  to  a  hook,  F,  and  gradually 
drawn  out. 

The  production  of  calcium  by  the  Virginia  Electrolytic  Com- 
pany in  1907  was  350  pounds,  valued  at  $613,  and  about  the 
same  amount  was  produced  in  1908. 6 

6  Min.  Ind.  17,  99,  (1908). 
'Min.  Ind.  16,  131,  (1907). 
»  U.  S.  Pat.  880,760. 


CHAPTER   XIII 

THE  ELECTROMETALLURGY  OF  IRON  AND  STEEL 
1.    GENERAL  DISCUSSION 

BEFORE  giving  an  account  of  the  application  of  electric  heat- 
ing to  the  iron  and  steel  industry,  a  short  sketch  of  the  older 
methods  of  winning  and  refining  iron  will  not  be  out  of  place. 

The  extraction  of  iron  from  its  ores,  consisting  principally  of 
oxides  of  iron  mixed  with  clay,  silica,  and  other  impurities,  is 
accomplished  by  reducing  the  ore  with  some  form  of  carbon,  usu- 
ally coke.  This  operation  is  carried  out  in  a  blast  furnace,  a  cir- 
cular brick  structure  lined  with  silicious  brick,  and  varying  in 
size  from  48  feet  to  106  feet  in  height,  and  from  8  feet  to  15 
feet  in  diameter  at  the  base.  Figure  97  shows  the  elevation  of  a 
blast  furnace.  It  consists  of  three  principal  parts :  (1)  the  cru- 
cible or  hearth  at  the  base,  cylindrical  in  shape,  (2)  the  bosh 
directly  above,  which  gradually  widens,  and  (3)  the  stack,  from 
which  point  the  furnace  contracts  for  the  rest  of  its  height. 
The  furnace  is  filled  with  alternate  layers  of  ore,  coke,  and  flux, 
the  latter  usually  consisting  of  calcium  carbonate.  The  object 
of  the  flux  is  to  form  a  fusible  slag  with  the  constituents  of  the 
ore  which  are  not  reduced  by  the  carbon,  such  as  silica  and 
alumina.  The  heat  necessary  to  raise  the  charge  to  a  temper- 
ature high  enough  for  reduction  is  produced  by  the  combustion 
of  the  coke  in  the  charge,  by  means  of  air  forced  in  through  the 
tuyeres,  F,  projecting  through  the  wall  of  the  furnace  just  below 
the  bosh.  The  carbon  therefore  serves  the  double  purpose  of 
furnishing  the  heat  and  of  reducing  the  ore. 

The  highest  temperature  of  the  furnace  is  near  the  tuyeres 
and  a  few  feet  above  them ;  in  this  region  the  slag  and  iron 
melt  and  drop  into  the  crucible,  where  they  separate,  the  slag 

239 


240 


APPLIED   ELECTROCHEMISTRY 


floating  on  the  iron.  These  are  drawn  off  from  time  to  time 
through  the  tap  holes  Or  and  H,  and  fresh  material  is  fed  into 
the  top  of  the  furnace  by  mechanical  means.  The  iron  thus 


FIG.  97.  — Elevation  of  blast  furnace 

produced  is  known  as  pig  iron,  and  contains  from  three  to  four 
per  cent  of  carbon,  as  much  as  four  per  cent  of  silicon,  and  one 
per  cent  of  manganese,  and  a  few  hundredths  of  one  per  cent  of 
sulphur  and  phosphorus.  Only  about  23  per  cent  of  the  pig 
iron  made  in  this  country  is  used  without  subsequent  purifica- 
tion.1 Purification  or  refining  of  iron  is  accomplished  by  oxi- 
dizing the  impurities  and  causing  them  to  form  a  slag,  which 
floats  on  the  iron. 

1  Stoughton,  The  Metallurgy  of  Iron  and  Steel,  p.  52. 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL        241 

One  method  of  refining  consists  in  blowing  air  through  the 
liquid  metal  in  a  Bessemer  converter.  The  lining  of  the  con- 
verter may  be  either  basic,  consisting  of  calcined  dolomite  (cal- 
cium and  magnesium  oxides),  or  acid,  consisting  of  silica.  The 
Bessemer  method  is  very  rapid,  silicon  and  manganese  oxidizing 
in  about  four  minutes  from  the  time  when  the  air  is  first  blown 
in.  The  carbon  then  begins  to  oxidize  to  carbon  monoxide, 
which  boils  up  through  the  metal  and  comes  out  of  the  con- 
verter in  a  long  flame.  In  about  six  minutes  from  the  time  the 
carbon  begins  to  oxidize,  it  is  reduced  to  approximately  0.04 
per  cent,  and  the  operation  is  then  stopped.  The  temperature 
is  higher  at  the  end  of  the  process  than  at  the  start,  due  to 
the  heat  of  oxidation  of  the  impurities.  A  calculated  amount 
of  carbon  is  then  added,  also  1.5  per  cent  of  manganese  to 
remove  the  oxygen,  and  0.2  per  cent  of  silicon  to  remove  the 
other  gases.  The  steel  is  then  cast  into  molds. 

The  second  method  of  refining  is  known  as  the  open  hearth  or 
Siemens-Martin  process.  This  consists  in  melting  the  pig  iron 
in  a  large  reverberatory  furnace,  whose  lining  may  be  either 
basic  or  acid.  The  oxidation  of  the  impurities  is  brought  about 
by  the  excess  of  oxygen  in  the  furnace  gases  over  that  neces- 
sary to  burn  the  gases.  A  much  longer  time  is  required  for 
purification  by  the  open  hearth  than  by  the  Bessemer  process. 
In  the  basic  open  hearth  process  enough  lime  is  added  to  form 
a  very  basic  slag,  which,  unlike  an  acid  slag,  will  dissolve  phos- 
phorus. The  lining  must  also  be  basic  to  prevent  its  being 
eaten  away  by  the  basic  slag. 

The  third  method  of  purification  is  known  as  the  puddling 
process,  in  which  the  iron  is  melted  on  the  hearth  of  a  rever- 
beratory furnace  lined  with  oxides  of  iron.  The  pig  iron  is 
charged  by  hand  through  the  doors  of  the  furnace  and  is  melted 
as  quickly  as  possible.  During  melting,  silicon  and  manganese 
go  into  the  slag,  as  well  as  some  of  the  oxide  of  the  lining. 
Iron  oxide  is  then  added  in  order  to  make  a  very  basic  slag ; 
the  charge  is  thoroughly  mixed,  and  the  temperature  is  lowered 
to  the  point  where  the  slag  begins  to  oxidize  the  phosphorus 
and  sulphur  before  the  carbon.  After  the  removal  of  these 


242  APPLIED   ELECTROCHEMISTRY 

impurities,  the  carbon  begins  to  oxidize  and  comes  off  as  carbon 
monoxide,  which  burns  on  coming  in  contact  with  the  air. 
During  this  time  the  puddler  stirs  the  charge  vigorously  with  a 
long  iron  rabble,  an  instrument  shaped  like  a  hoe.  As  the  iron 
becomes  pure,  its  melting  point  rises  and  it  begins  to  solidify, 
since  the  temperature  of  the  furnace  is  below  the  melting  point 
of  pure  iron.  The  iron  is  finally  removed  in  the  form  of  a  ball 
dripping  with  slag,  and  is  put  through  a  squeezer  to  remove  the 
slag  as  much  as  possible.  This  product  is  known  as  wrought 
iron.  It  is  converted  into  steel  by  two  methods,  (1)  the  ce- 
mentation, and  (2)  the  crucible  process.  In  the  cementation 
process  the  wrought  iron  is  carburized  by  heating,  without 
melting,  in  contact  with  carbon.  The  carbon  slowly  penetrates 
the  iron  and  changes  it  to  steel.  In  the  crucible  process  the 
wrought  iron  is  cut  up  into  small  pieces  and  is  melted  in  covered 
crucibles  with  the  desired  amount  of  carbon  or  other  element 
that  is  to  be  alloyed  with  it.  When  the  process  is  finished  the 
steel  is  cast  into  molds.  By  thus  remelting  the  iron,  the  slag 
is  removed  and  the  required  amounts  of  carbon,  silicon,  and 
manganese  are  added. 

2.    THE  ELECTROTHERMIC  REDUCTION  OF  IRON  ORES 

The  conditions  under  which  electric  heating  can  economically 
be  substituted  for  the  heat  of  combustion  of  coke  in  the  reduc- 
tion of  iron  ores  are  purely  local.  In  places  where  iron  ore 
can  be  obtained  cheaply,  where  metallurgical  coke  is  expensive, 
where  water  power  is  cheap,  and  where  iron  would  have  to  be 
hauled  from  a  great  distance  to  supply  the  local  demand,  it 
may  be  possible  to  produce  iron  by  electric  heating  at  a  price 
low  enough  to  compete  with  that  brought  from  a  distance. 
These  conditions  exist  in  Canada,  Sweden,  and  California.1 

The  first  attempt  to  apply  electric  heating  to  the  metallurgy 
of  iron  was  made  in  1853  by  Pinchon,2  and  in  1862  Monkton 
took  a  patent  in  England  for  the  reduction  of  ores  by  the 

1  Eugene  Haanel,  Trans.  Am.  Electrochem.  Soc.  15,  25,  (1909)  l  and  P.  McN. 
Bennie,  ibid.  p.  35. 

2  B.  Neumann,  Electrometallurgie  des  Eisens,  p.  3,  (1907). 


THE  ELECTROMETALLURGY  OF  IRON  AND  STEEL   243 


FIG.  98.  —  Stassano's  first  furnace  at  Rome 


electric  current.  Sir  Wil- 
liam Siemens  again  called 
attention  to  this  subject 
in  a  lecture  before  the 
Society  of  Telegraph  En- 
gineers in  London  in  1880. 3 
The  first,  however,  to  show 
by  experiments  on  a  large 
scale  that  iron  can  be  re- 
duced commercially  by 
electric  heating  was  the 
Italian  army  officer,  Major 
Stassano.4  Patents  were 
taken  out  by  him  in  the  year  1898  in  different  countries,  con- 
sequently this  date 
marks  the  beginning 
of  the  actual  appli- 
cation of  electricity 
to  the  metallurgy  of 
iron.  The  contrac- 
tion of  the  carbide 
industry  in  1899  to 
1900,  due  to  over- 
production, leaving 
idle  a  number  of 
water-power  stations 
in  southeastern 
France,  for  which 
some  new  application 
of  electric  power  was 
needed,  also  hastened 
the  introduction  of 
electric  heating  in  the 
iron  industry.6 

Stassano's    prelim- 


FIG.  99.  —  Horizontal  section  of  Stassano's  electric 
furnace  at  Darfo 


»  Elektrotech.  Z.  1,  325,  (1880). 

4  Askenasy,  Technische  Elektrochemie,  94,  (1910). 

6  J.  B.  C.  Kershaw,  Electrometallurgy,  p.  175,  (1908). 


244 


APPLIED   ELECTROCHEMISTRY 


inary  experiments  on  the  reduction  of  iron  ore  were  carried 
out  at  Rome  in  1898,6  with  the  150  horse  power  furnace  repre- 
sented in  Figure  98.  It  is  seen  to  resemble  an  ordinary  blast 
furnace.  Since  there  was  no  combustion  of  carbon,  no  reduc- 
ing gases  were  produced ;  consequently,  in  order  to  bring  the 


FIG.  100.  —  Vertical  section  of  Stassano's  electric  furnace  at  Darfo 

carbon  and  ore  in  intimate  contact,  they  were  powdered,  mixed, 

and  made  into  briquettes  with  pitch  as  a  binder.     The  furnace 

6  See  an  article  by  Stassano  reprinted  in  Haanel's  Keport,  p.  178,  (1904). 


THE  ELECTROMETALLURGY  OF  IRON  AND  STEEL   245 


was  first  heated  without  a  charge ;  an  iron  grating  was  then 
placed  in  the  furnace  20  centimeters  above  the  arc,  and  the  mix- 
ture was  charged  in  from  the  hopper  at  the  top  and  was  held 
up  by  the  grating.  The  grating  eventually  melted,  and  the 
ore  in  contact  with  it  was  reduced.  In  this  state  the  mixture 
which  lay  on  the  grating  became  fused  and  formed  an  arch, 
which  supported  the  charge  even  when  the  grating  melted 
away.  As  the  heat  from  the  arc  penetrated  the  mass  above  the 
arch,  iron  was  reduced  and  dropped  into  the  crucible  below. 
In  the  course  of  twelve  hours  the  arch  increased  so  in  thickness, 
due  to  the  slag  produced,  that  it  prevented  the  efficient  heat- 
ing of  the  charge  above.  Consequently  this  form  of  furnace 
was  given  up,  and  one  was  adopted  in  which  the  material  was- 
introduced  below  the  arc,  as  is  done  in  refining  furnaces.  The 
final  form  adopted  at  Darfo, 
in  northern  Italy,  is  shown 
in  Figures  99  and  100. 
Movement  of  the  entire 
chamber  in  which  the  fu- 
sion takes  place  is  effected 
by  rotating  about  an  axis 
inclined  to  the  vertical. 
The  electricity  is  conducted 
to  the  furnace  by  sliding 
contacts  on  two  metal  rings 
at  the  top  of  the  furnace. 
This,  furnace  worked  per- 
fectly satisfactorily,  even 
when  run  for  several  days. 
The  most  difficult  ques- 
tions to  decide  were  the  re- 
lation between  the  size  of  the  cavity  and  the  energy  to  be 
supplied,  and  the  manner  of  making  the  refractory  lining.  The 
carbon  electrodes  were  1.5  meters  long  and  lasted  sixty  consec- 
utive hours.  The  furnace  was  supplied  with  1000  amperes  at 
100  volts,  and  since  the  value  of  the  cosine  of  the  phase  differ- 
ence between  electromotive  force  and  current  was  0.8,  the  power 


FIG.  101.  — The  Keller  electric  furnace  for 
reducing  iron  ore 


246  APPLIED   ELECTROCHEMISTRY 

consumed  was  80  kilowatts.  The  best  yield  with  this  furnace 
was  one  kilogram  of  soft  iron  for  3.2  kilowatt  hours,  and  the 
iron  obtained  was  always  over  99  per  cent  pure.  The  ore, 
which  was  from  the  island  of  Elba,  had  the  following  com- 
position : 

Fe2O3 93.020  per  cent 

MnO 0.619  per  cent 

SiO2 3.792  per  cent 

CaO,  MgO 0.500  per  cent 

Sulphur ,  0.058  per  cent 

Phosphorus 0.056  per  cent 

Moisture 1.720  per  cent 

According  to  Stassano,  the  plant  at  Darfo  was  shut  down 
for  reasons  not  directly  connected  with  the  success  of  the 
process. 

The  Keller  furnace  for  making  pig  iron  is  shown  in  Figure 
101.  This  furnace  was  seen  in  operation  by  the  Canadian 
Commission  at  Livet,  France,  in  1904.  ItT  consists  of  two 
iron  castings  of  square  cross  section,  forming  two  shafts  com- 
municating with  each  other  at  their  lower  ends  by  a  lateral 
canal.  The  castings  are  lined  with  refractory  material.  The 
base  of  each  shaft  is  provided  with  a  carbon  block,  these  two 
blocks  being  connected  to  each  other  outside  the  furnace  by 
copper  bars.  On  starting,  before  there  is  metal  in  the  canal, 
the  current  flows  from  one  block  to  the  other  through  the  copper 
bar,  but  when  enough  metal  has  been  reduced  to  partially  fill 
the  canal,  most  of  the  current  flows  through  the  melted  metal. 
The  electrodes  are  1.4  meters  long  and  85  by  85  centimeters  in 
cross  section.  The  cost  of  electrodes  per  metric  ton  of  pig  iron 
is  estimated  by  Keller  at  3.85  francs.  The  energy  absorbed 
per  metric  ton  of  pig  iron  in  a  furnace  supplied  with  11,000 
amperes  at  60  volts  was  0.390  kilowatt  year  for  the  run,  and 
with  a  smaller  furnace  supplied  with  7000  amperes  at  55  volts 
it  was  0.186  kilowatt  year  for  the  run.8 

»  Haanel's  Report,  p.  15,  (1904).  «  Haanel's  Report,  p.  20,  (1904). 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL       247 


.EXPERIMENTAL. 
ElZCTRICfURNACt 


Following  the  tour  of  inspection  by  the  Canadian  Commission, 
an  investigation  was  carried  out  for  the  Canadian  government 
in  1906  by  Heroult,  to  see  (1)  whether  magnetite  could  be  eco- 
nomically smelted  by  the  electrothermic  process ;  (2)  whether 
ores  containing  sulphur,  but  not  manganese,  could  be  made  into 
pig  iron  of  marketable  composition  ;  and  (3)  whether  charcoal 
could  be  substituted  for  coke.  The 
furnaces  were  slightly  modified  as  the 
investigation  proceeded,  and  the  final 
form  is  shown  in  Figure  102.  It 
consists  of  a  cylindrical  iron  casting 
|  inch  thick,  bolted  to  a  bottom  plate 
of  cast  iron  48  inches  in  diameter. 
The  casting  was  made  in  two  sections 
bolted  together  by  angle  irons.  In 
order  to  make  inductance  small,  the 
magnetic  circuit  was  broken  by  re- 
placing a  vertical  strip  of  10  inches 
width  in  the  casting  by  copper.  Rods 
of  iron  were  cast  into  the  bottom  plate 
to  secure  good  contact  with  the  car- 
bon paste  rammed  into  the  lower  part 
of  the  furnace.  The  electrodes,  6 
feet  long  and  16  by  16  inches  in  cross 
section,  were  manufactured  by  a  pro- 
cess of  Heroult's  and  were  imported 
from  Sweden.  The  pipe  k  was  for  the  purpose  of  cooling  the 
electrode  holder  by  a  current  of  air.  The  current  was  between 
4000  and  5000  amperes  at  36  to  39  volts,  and  the  power  factor 
was  0.919.  The  ores  used  in  the  experiments  below  were  of 
the  following  composition: 


FIG.  102.  —  Heroult  experimen- 
tal furnace  at  Sault  Ste. 
Marie,  for  reducing  iron  ore 


248 


APPLIED   ELECTROCHEMISTRY 


TABLE  30 
Composition  of  Ores  investigated  by  Heroult  for  the  Canadian  Government 


HEMATITE 

MAGNETITE 

ROASTED 
PYRRHOTITE 

TlTANIPEROUS 

IRON  ORE 

1 

2 

3 

Fe 

62.23 

56.69 

55.85 

58.29 

45.80 

43.59 

SiO2 

5.42 

6.20 

6.60 

4.00 

10.96 

7.12 

Fe203 
FeO 
A1203 

88.90 

55.42 
23.04 
2.56 

60.74 
17.18 
1.48 

55.31 
25.20 
2.24 

65.43 
3.31 

30.30 
28.78 
7.00 

2.51 

CaO 

0.61 

2.00 

2.48 

2.40 

3.92 

1.00 

MgO 
Mn 

0.30 
0.16 

6.84 

5.50 

4.00 

3.53 

4.14 

MnO 



0.258 

0.13 







P 

0.044 

0.01 

0.016 

0.415 

0.016 

0.028 

S 

0.0002 

0.05 

0.57 

0.45 

1.56 

0.04 

CO2    and    unde- 
termined 
Loss  on  ignition 
Cu 
Ni 

3.609 

4.923 

M6 

2.23 



2.48 



TiO2 











17.82 

100.426 

100.00 

100.00 

100.00 



99.648 

The  consumption  of  the  electrode  in  these  experiments  was 
8.9  kilograms  per  metric  ton  of  pig  iron  produced.     The  yield 
per  unit  of  energy  vafried  somewhat,  but  was  approximately 
0.25  kilowatt  year  of  365  days  per  metric  ton  of  pig  iron. 
The  results  of  these  experiments  were  : 

1.  Canadian  ores,  chiefly  magnetites,  can  be  as  economically 

smelted  as  hematites  by  the  electrothermic  process. 

2.  Ores  of  high  sulphur  content  can  be  made  into  pig  iron 

containing   only  a  few  thousandths  of  one  per  cent  of 
sulphur. 

3.  The  silicon  content  can  be  varied  as  required  for  the  class 

of  pig  iron  to  be  produced. 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL        249 

4.  Charcoal  which  can  be  cheaply  produced  from  mill  refuse 

or  wood  which  could  not  otherwise  be  utilized,  and  peat 
coke,  can  be  substituted  for  coke  without  being  briquetted 
with  the  ore. 

5.  A  ferro-nickel  pig  can  be  produced  practically  free  from 

sulphur,  and  of  fine  quality,  from  roasted  nickeliferous 
pyrrhotite. 

6.  Titaniferous  iron  ores  containing  up  to  five  per  cent  can 

be  successfully  treated  by  the  electrothermic  process. 

These  results  demonstrated  the  feasibility  of  applying  the 
electrothermic  process  to  the  reduction  of  iron  ores.9  All  that 
was  necessary  to  put  it 
on  a  commercial  basis 
was  the  construction  of 
a  furnace  that  could  be 
economically  and  suc- 
cessfully used  in  prac- 
tice. This  was  under- 
taken by  three  Swedish 
engineers,  Messrs.  Gron- 
wall,  Lindblad,  and  Stal- 
hane,  at  Domnarfvet, 
Sweden.  They  concen- 
trated their  attention  on 
the  construction  of  a 
furnace  following  the 
suggestions  contained  in 
the  report  of  Heroult's 
experiments  for  the 


Canadian  government, 
which  were,  (1)  charg- 
ing by  labor-saving  ma- 
chinery, (2)  collection 
and  use  of  carbon  monoxide  produced  by  the  reduction  of  the 
ore,  (3)  automatic  regulation  of  electrodes,  and  (4)  a  sufficiently 


fire  BricA  £3  Masncsitt 
FIG.  103.  —  Electric  furnace  at  Domnarfvet,  Swe- 
den, for  reducing  iron  ore 


9  Haanel,  Trans.  Ain.  Electrochem.  Soc.  15,  25,  (1909). 


250  APPLIED   ELECTROCHEMISTRY 

high  shaft  containing  the  charge  to  permit  the  heated  carbon 
monoxide  to  produce  the  maximum  reduction  of  the  ore. 
Seven  furnaces  were  constructed  and  tested  before  arriving  at 
the  one  which  they  considered  practical  and  commercial.  This 
required  over  two  years  and  an  expenditure  of  $  102,000. 1(> 
A  vertical  section  of  the  furnace  is  shown  in  Figure  103,  from 
which  the  general  construction  is  perfectly  obvious.  It  evi- 
dently resembles  somewhat  Stassano's  original  furnace,  and, 
like  his,  is  started  as  an  ordinary  blast  furnace.10  The  crucible 
is  2.25  meters  in  diameter  and  1.5  meters  high.  The  most 
important  point  in  the  construction  is  the  manner  in  which 
the  electrodes  are  brought  into  the  melting  chamber.  As  seen 
from  the  section,  they  enter  through  that  portion  of  the  roof  of 
the  crucible  that  does  not  come  in  contact  with  the  charge, 
and  pass  into  the  charge  at  the  slope  formed  by  the  materials 
of  which  it  is  composed.  The  electrodes  dip  into  the  charge, 
but  not  into  the  melted  iron  beneath  it.11  Experiments  had 
shown  that  the  brickwork  lining  around  the  electrodes  was  al- 
ways destroyed  if  brought  in  contact  with  the  charge,  even 
when  the  electrodes  were  water  cooled.  The  brickwork  com- 
posing the  lining  of  the  roof  of  the  melting  chamber  was 
cooled  by  forcing  against  it,  through  tuyeres,  the  compara- 
tively cool  tunnel-head  gases.  The  heat  absorbed  by  these 
gases  is  given  back  to  the  charge  above. 

A  three-phase  current  is  supplied  to  three  electrodes  11  by 
22  inches  in  cross  section  and  63  inches  in  length.  The  water- 
cooled  stuffing  boxes  through  which  the  electrodes  enter  the 
melting  chamber  are  provided  with  devices  to  prevent  the  hot 
gases  under  pressure  from  leaking  out  around  the  electrodes. 
The  results  of  a  short  run  that  was  made  in  the  presence  of 
Dr.  Haanel  showed  (1)  that  the  furnace  operated  uniformly 
and  without  trouble  of  any  kind  for  five  consecutive  days,  the 
electrodes  requiring  no  adjustment  whatever;  (2)  that  the 
energy  consumption  was  remarkably  uniform ;  (3)  that  a  free 

10  For  the  evolution  of  the  furnace,  and  dimensions,  see  Met.  and  Chem, 
Eng.  8,  11,   (1910). 

11  Assar  Gronwall,  Electrochem.  and  Met.  Ind.  7,  420,  (1900). 


THE    ELECTROMETALLURGY   OF   IRON   AND    STEEL        251 


space  was  maintained  between  the  charge  and  the  roof  of  the 
heating  chamber  ;  (4)  that  the  charge  did  not  jam  at  the  lower 
contracted  neck  of  the  shaft,  but  moved  with  regularity  into 
the  melting  chamber;  and  (5)  that  the  lining  of  the  roof  of 
the  melting  chamber  was  effectively  cooled  by  the  circulation 
of  gas. 

Since  the  short  run  witnessed  by  Dr.  Haanel,  the  furnace  has 
been  in  continual  operation 
for  85  days,  and  met  all  the 
requirements  that  indicate  a 
durable  furnace.10  The  de- 
signers of  this  furnace  have 
contracted  to  erect  three  large 
furnaces  for  the  reduction  of 
iron  ores  at  Sault  Ste.  Marie, 
Canada,  to  be  in  operation  by 
the  middle  of  1910.12  The 
first  electric  smelting  plant  in 
Canada  was  under  construc- 
tion at  Welland,  Ontario,  in 
1907.13  It  was  to  consist  of 
a  3000  horse  power  furnace 
of  the  latest  type  brought  out 
by  Heroult. 

In  1909  an  electrothermic 
plant  for  reducing  iron  ore 
was  in  existence  on  the  Pitt 
River  at  Heroult,  Shasta 
County,  California."  From  the 
section  of  this  1500  kilowatt 
furnace  shown  in  Figure  104,  its  resemblance  to  the  furnace  at 
Domnarf vet  will  be  evident.  A  general  view  is  shown  in  Fig- 
ure 105.  Though  this  furnace  is  on  a  commercial  scale,  in 
July,  1910,  it  was  still  in  the  experimental  stage,  on  account 

12  Electrochem.  and  Met.  Ind.  7,  535,  (1909). 

is  Haanel's  Report,  1907,  p.  147. 

"  D.  A.  Lyon,  Trans.  Am.  Electrochem.  Soc.  15,  39,  (1909). 


252  APPLIED   ELECTROCHEMISTRY 

of  numerous  difficulties  that  had  been  encountered.  Several 
changes  have  been  made  and  it  is  expected  that  the  furnace 
will  be  perfected  shortly.  When  this  is  accomplished,  the 
Noble  Electric  Steel  Company  will  build  four  or  five  others 
of  a  similar  type.15  Pig  iron  on  the  Pacific  coast  brings  $23 
to  $26  a  ton,16  and  the  cost  from  this  furnace  is  expected  to 
be  $15  a  ton,  which  leaves  a  good  margin  of  profit. 

3.    THE  ELECTROTHERMIC  REFINING  OF  STEEL 

While  the  application  of  electrothermics  to  the  reduction  of 
pig  iron  is  scarcely  an  established  commercial  industry,  the  case 
is  quite  the  reverse  in  steel  refining,  for  a  large  number  of  fur- 
naces for  this  purpose  are  in  operation  in  Europe  and  America. 
Even  in  this  case,  however,  the  electric  furnace  cannot  compete 
with  the  Bessemer  or  with  the  open-hearth  process  for  making 
structural  steel.  Electric  furnace  refining  is  used  only  to  pro- 
duce very  high-class  steel  for  special  purposes,1  for  which  it  is 
far  superior  to  the  crucible  process,  on  account  of  the  greater 
cheapness  and  higher  quality  of  the  steel  produced.2  The 
reason  for  the  better  quality  of  the  product  is  that  the  atmos- 
phere is  neutral,  and  a  much  higher  temperature  can  be  obtained 
than  by  other  means,  resulting  in  a  more  complete  removal  of 
impurities,  especially  gases.  Phosphorus  and  sulphur  disap- 
pear nearly  completely,  and  deoxidation  is  more  complete 
than  that  attained  by  any  other  means.  Another  advantage 
of  electric  heating  is  the  reliability  and  certainty  of  the 
process.3 

A  number  of  different  electric  furnaces  have  been  designed 
for  refining  steel,  and  some  of  the  principal  ones  will  now  be 
described. 

15  private  communication  from  Professor  D.  A.  Lyon,  the  manager  of  the 
company. 

16  Bennie,  Trans.  Am.  Electrochem.  Soc.  15,  36,  (1909). 

1  Haanel's  Report,  (1904),  p.  31;  Hibbard,  Trans.  Am.  Electrochem.  Soc.  15, 
231,  (1909). 

2  Askenasy,  Technische  Elektrochemie,  p.  56,  (1910). 

3  Askenasy,  Technische  Elektrochemie,  p.  156,  (1910). 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL        253 


FIG.  105.  —  Electric  furnace  at  Heroult,  California,  for  reducing  iron  ore 


254  APPLIED   ELECTROCHEMISTRY 

The  furnace  used  by  Stassano  at  his  works  in  Turin  is 
similar  to  the  one  he  finally  adopted  for  reducing  iron  ore4 
(Figures  99  and  100).  The  charge  is  heated  by  radiation 
from  arcs  formed  between  three  electrodes  placed  above  the 
charge  and  supplied  with  a  three-phase  current.  This  furnace 
also  rotates  on  an  axis  slightly  inclined  to  the  vertical,  in  order 
to  mix  the  charge  thoroughly.  The  lining  is  magnesite  brick. & 
Starting  with  scrap  and  oxidized  turnings,  about  one  kilowatt 
hour  is  required  for  one  kilogram  of  finished  steel  in  the  250 
horse  power  furnaces  used  at  Turin. 

A  furnace  designed  by  Charles  Albert  Keller  for  steel  refin- 
ing, which  was  put  into  industrial  use  in  1907,  is  shown  in 
Figures  106  and  107.  It  consists  of  a  crucible  with  a  conduct- 
ing bottom  for  one  electrode  and  a  vertical  carbon  rod  for  the 
other.6  Since  carbon  must  not  be  brought  in  contact  with 
the  melted  iron  in  refining,  the  bottom  must  be  made  conduct- 
ing without  the  use  of  carbon,  and  this  was  accomplished  by 
Keller  as  follows  :  Iron  bars  from  1  to  1|  inches  in  diameter 
are  regularly  spaced  about  one  inch  apart,  and  are  made  fast  to 
a  metallic  plate  at  the  bottom,  covering  the  entire  area  on  which 
the  bath  will  rest.  Agglomerated  magnesia  is  then  rammed, 
while  hot,  in  between  the  bars.  The  whole  base  is  surrounded 
by  a  metallic  casing  for  water  cooling.  Electrical  contact  is 
made  by  the  lower  plate  to  which  the  bars  are  fastened.  The 
furnace  is  closed  by  a  cover  through  which  the  other  electrode 
passes.  After  several  months'  use  a  hearth  constructed  in  this 
manner  was  found  to  be  in  as  good  condition  as  on  the  first 
day.  The  advantage  claimed  for  this  arrangement  over  a 
furnace  with  two  vertical  electrodes  is  that  the  current  is  more 
evenly  distributed  through  the  charge,  and  consequently  heats 
it  more  evenly.  Of  course,  the  iron  bars  are  melted  at  their 
upper  ends  where  they  come  in  contact  with  the  melted  iron  to 
be  refined,  but  the  water  cooling  prevents  them  from  melting 
for  more  than  a  few  inches  of  their  length. 

4  Trans.  Am.  Electrochem.  Soc.  15,  63,  (1909). 
6  Trans.  Am.  Electrochem.  Soc.  15,  86,  (1909). 
6  Trans.  Am.  Electrochem.  Soc.  15,  96,  (1909). 


THE   ELECTROMETALLURGY   OF   IRON   AND    STEEL        255 


I  _  1 


> 

/    »•<£•*  •••V»v^;«oc.a> 


FIGS.  106  and  107.  —  Keller  conducting  hearth  furnace 


256 


APPLIED   ELECTROCHEMISTRY 


The  Heroult  steel  refining  furnace,7  as  shown  in  Figure  108, 
consists  of  a  crucible  a  with  a  cover  b  holding  a  small  chimney 
c.  As  the  figure  shows,  it  is  arranged  for  tilting,  d  are  car- 
bon electrodes,  which  may  be  moved  in  a  vertical  or  in  a  hori- 
zontal direction.  In  order  to  use  the  furnace  for  Bessemer- 


FIG.  108.  —  The  Heroult  electric  steel  furnace 

izing,  the  tuyeres  x  are  provided.  The  two  electrodes  do  not 
quite  touch  the  slag  on  the  surface,  so  that  two  arcs  are  pro- 
duced. In  passing  through  the  bath,  the  current,  of  course, 
divides  between  the  slag  and  the  melted  iron  in  proportion  to 
their  conductivities,  and  as  melted  iron  conducts  better  than 
the  slag,  a  larger  proportion  would  flow  through  the  metal  than 
through  the  slag.  The  poorest  kinds  of  scrap,  high  in  sulphur 
and  phosphorus,  are  refined  in  this  furnace.  The  following 
table  shows  the  average  refining  ability  of  a  2  J-ton  furnace  at 
La  Praz,  Savoy  : 

7  Electrochem.  Ind.  1,  64,  (1902)  ;  U.  S.  Pat.  707,776. 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL       257 
TABLE  31 


PEE  CENT 

Sulphur 

Phosphorus 

Manganese 

Silicon 

Carbon 

Scrap  charged 
Finished  steel 

0.052 
0.006 

0.150 
0.009 

0.638 
0.254 

0.062 
0.172 

0.211 
1.013 

For  a  5-ton  furnace,  starting  with  cold  scrap,  600  kilowatt 
hours  are  necessary  to  partially  refine  one  long  ton  of  steel, 
and  100  more  for  the  finishing  slag.  For  a  15-ton  furnace, 
less  power  would  be  required. 

Figure  109  shows  a  15-ton  three-phase  Heroult  furnace  at 
the  South  Chicago  Works  of  the  Illinois  Steel  Company. 
The  steel  to  be  treated  is  brought  directly  from  the  Bessemer 
converters,  and  two  refining  slags  are  used  in  the  electric 
furnace,  the  first  an  oxidizing  slag  to  take  out  the  phosphorus, 
and  the  second,  a  deoxidizing  slag  for  removing  the  sulphur 
and  the  gases.8  Power  is  supplied  to  the  three  electrodes  by 
three  transformers,  each  of  750  kilowatts  capacity.  Two 
hundred  and  forty  tons  of  steel  are  turned  out  per  day  in  16 
heats.  The  electrodes,  2  feet  in  diameter  and  10  feet  in  length, 
are  the  largest  ever  made  in  one  piece.  In  cold  melting  and  in 
continuous  work,  the  consumption  of  electrode  is  from  60  to  65 
pounds  per  ton  of  steel,  but  when  the  metal  is  charged  in  the 
melted  state,  the  consumption  would  be  reduced  to  10  or  15 
pounds  per  ton  of  steel.  This  includes  the  short  ends  that 
cannot  be  utilized.  The  linings  last  from  three  months  to 
one  year,  depending  on  the  care  with  which  the  furnace  is  run; 
the  roof  suffers  most,  and  generally  has  to  be  renewed  once  a 
month.  The  best  lining  for  this  furnace  is  magnesite  mixed 
with  basic  slag,  with  tar  for  a  binder. 

The  Paul  Girod  electric  furnace  9  is  somewhat  similar  to  the 
Keller  furnace,  as  seen  from  Figure  110.  One  or  more  elec- 


8  Robert  Turnbull,  Trans.  Am.  Electrochem.  Soc.  15,  139,  (1909). 

9  Paul  Girod,  Trans.  Am.  Electrochem.  Soc.  15,  127,  (1909). 


258 


APPLIED    ELECTROCHEMISTRY 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL       259 


trodes  of  like  polarity  are  suspended  above  the  crucible,  while 
the  electrode  of  opposite  polarity  consists  of  a  number  of  pieces 
of  soft  steel  buried  in  the  refractory  material  of  the  hearth  at 
its  periphery  and  water  cooled  at  their  lower  ends.  The 
upper  ends  come  in  contact  with  the  bath  and  are  melted  to  a 
depth  of  2  to  4  inches.  About  55  volts  are  applied  to  this 
furnace.  For  fusing,  refining, 
and  finishing  a  charge  of  cold 
scrap  in  a  2-ton,  furnace,  about 
900  kilowatt  hours  per  metric 
ton  of  steel  are  required,  and  in 
an  8  to  10  ton  furnace,  700  kil- 
owatt hours.  The  electrode  con- 
sumption is  16  to  18  kilograms 
per  metric  ton  of  steel  produced 
in  a  2-ton  furnace,  and  13  to  15 
kilograms  in  an  8  to  10  ton  fur- 
nace. The  short  ends  are  in- 
cluded as  having  been  used.  The 
lining  is  magnesite  or  dolomite 
brick  or  paste,  and  lasts  40  to  50 
heats  without  any  repairs  what- 
ever. 

An  entirely  different  class  of 
steel-refining  furnaces  are  those 
having  the  melted  metal  in  the 
form  of  a  ring,  forming  the  sec- 
ondary of  a  transformer  which  is 
heated  by  an  induced  current 
from  a  primary  coil  of  copper 
wire.  This  type  of  furnace  was 
patented  in  1887  by  Colby  in  the 
United  States  and  by  Ferranti 
in  England.  The  same  principle  was  applied  on  a  small  scale 
in  1900  by  F.  A.  Kjellin  at  Gysinge,  Sweden,  without  knowing 
at  the  time  that  it  had  been  patented  by  others.10  Kjellin, 
10  Kjellin,  Trans.  Am.  Electrochem.  Soc.  15,  173,  (1909). 


Fia.  110.  —  The  Girod  electric  steel 
furnace 


260 


APPLIED   ELECTROCHEMISTRY 


however,  seems  to  have  been  the  first  to  carry  this  idea  out  on 
a  commercial  scale.  In  1902  a  225  horse  power  induction  fur- 
nace was  in  operation  at  Gysinge,  with  an  output  of  4  metric 
tons  in  24  hours.  This  furnace  had  a  magnesite  lining  in 


FIGS.  Ill  and  112.  —  Elevation  and  plan  of  the  Kjellin  induction  furnace 

place  of  silica  used  in  the  smaller  furnace.     A  silica  lining 
lasted  only  about  one  week,  while  the  magnesite  lasted  twelve. 


THE  ELECTROMETALLURGY  OF  IRON  AND  STEEL   261 

Figures  111  and  112  show  the  principle  of  the  Kjellin 
furnace.  The  magnetic  circuit  C  is  built  up  of  laminated 
sheet  iron.  D  is  the  primary  circuit,  consisting  of  a  number 
of  turns  of  insulated  copper  wire  or  tubing.  The  ring-shaped 
crucible  A,  for  holding  the  melted  metal,  is  made  of  refractory 
material.  This  furnace  cannot  be  started  by  placing  cold 
scrap  in  the  crucible  because  of  the  low  induced  electromotive 
force,  but  an  iron  ring  must  be  placed  in  the  crucible  and 
melted  down,  or  the  crucible  must  be  filled  with  melted  metal 
taken  from  another  source.  The  power  consumption  of  the 
furnace  at  Gysinge,  starting  with  cold  pig  iron  and  scrap,  is 
about  800  kilowatt  hours  per  metric  ton  of  product.  This 
furnace  has  been  found  very  satisfactory  for  making  the 
highest-class  steel  from  pure  raw  materials. 

There  is  a  limit  to  the  current  that  can  be  sent  through 
the  liquid  metal,  and  consequently  a  limit  to  the  temperature 
attainable.  This  is  due  to  a  phenomenon  first  observed  by 
Paul  Bary  in  1903,11  to  which  the  name  "  pinch  effect "  was 
given  by  Hering.12  This  phenomenon  is  as  follows  :  When  a 
direct  or  an  alternating  current  passes  through  a  liquid  con- 
ductor, the  conductor  tends  to  contract  in  cross  section,  forming- 
a  depression,  and  if  the  current  is  large  enough,  the  metal  in 
the  trough  will  separate  entirely  and  break  the  circuit.  This 
is  due,  of  course,  to  the  attraction  the  different  elements  of 
the  current  exert  on  each  other.  It  is  most  likely  to  happen 
at  some  particular  place  where  the  cross  section  of  the  ring  is 
smaller  than  elsewhere,  and  if  any  infusible  material  falls  into 
this  depression,  it  may  prevent  the  reunion  of  the  liquid  and 
cause  the  charge  to  .freeze.  The  largest  possible  current  that 
could  be  passed  through  liquid  iron  in  a  trough  2  inches  deep 
and  1  inch  wide  is  about  3300  amperes  ;  in  a  trough  4  by  2 
inches,  9400  amperes  ;  and  in  a  trough  6  by  3  inches,  17,000 
amperes.13  Larger  currents  would  cause  the  metal  to  separate 

11  Northrup,  Trans.  Am.  Electrochem.  Soc.  15,  303,  (1909). 

12  Hering,  Trans.  Am.  Electrochem.  Soc.  11,  329,  (1907)  j  15,  255  and  271, 
(1909). 

18  Trans.  Am.  Electrochem.  Soc.  15,  269,  (1909). 


262  APPLIED   ELECTROCHEMISTRY 

entirely.  When  a  depression  is  formed,  hydrostatic  pressure 
balances  the  pressure  due  to  the  current,  so  that  this  effect 
is  not  so  likely  to  give  trouble  in  a  deep  channel  as  in  a  shallow 
one,  nor  with  a  heavy  metal  as  with  a  light  one.  It  has  been 
found  impossible,  for  instance,  to  raise  aluminum  much  above 
its  melting  point,  in  a  60  kilowatt  induction  furnace  on  account 
of  this  effect.14 

The  Kjellin  furnace  is  not  adapted  to  working  with  dephos- 
phorizing and  desulphurizing  slags,  as  the  annular  ring  is  not 
a  convenient  shape  and  offers  too  small  a  surface  to  the  attack 
of  the  slag.15  A  combined  induction  and  resistance  furnace 
was  therefore  invented  by  Rodenhauser,  known  as  the  Rochling- 
Rodenhauser  furnace  for  refining  Bessemer  steel.  A  plan  and 
an  elevation  of  this  furnace  are  shown  in  Figures  113  and  114. 
HH  &VQ  the  two  legs  of  the  iron  transformer  core,  surrounded 
by  the  primary  windings  AA.  Surrounding  the  legs  of  the 
transformer  are  the  two  closed  circuits  of  melted  metal,  forming 
together  a  figure  8,  in  which  currents  are  induced.  BB  are 
two  extra  primary  coils,  from  which  the  current  is  conducted  to 
the  metallic  plates  EE.  These  are  covered  by  an  electrically 
conducting  refractory  material,  through  which  the  current  passes 
into  the  main  hearth,  D.  The  result  is  that  the  main  hearth 
can  be  made  with  a  much  larger  cross  section  than  the  ring  in 
the  original  Kjellin  furnace,  and  a  good  power  factor  can  be 
obtained  in  large  furnaces  without  such  a  low  periodicity  as 
was  necessary  with  the  original  induction  furnaces.  The  mag- 
nitude of  the  current  from  the  secondary  coils  is  limited  by  the 
carrying  capacity  of  the  refractory  material  6r,  which  would  be 
destroyed  if  too  heavily  loaded.  In  refining,  the  furnace  is 
worked  as  follows  :  Fluid  steel  from  the  converters  is  poured 
into  the  furnace,  and  burnt  limestone  and  mill  scale  are  added 
for  forming  a  basic  dephosphorizing  slag.  This  is  removed, 
after  the  reactions  are  ended,  by  tilting  the  furnace.  For  mak- 
ing rails  the  phosphorus  is  reduced  sufficiently  in  one  opera- 
tion, but  for  the  highest-class  steel  it  has  to  be  repeated. 

14  FitzGerald,  Trans.  Am.  Electrochem.  Soc.  15,  278,  (1909). 
16  Kjellin,  Trans.  Am.  Electrochem.  Soc.  15,  175,  (1909). 


THE    ELECTROMETALLURGY   OF   IRON   AND   STEEL       263 


FIGS.  113  and  114.  — Elevation  and  plan  of  the  Rochling-Rodenhauser  furnace 


264  APPLIED   ELECTROCHEMISTRY 

After  removing  phosphorus,  carbon  is  added  in  the  pure  state 
when  carbon  steel  is  to  be  made,  and  a  new  basic  slag  is  formed 
to  remove  the  sulphur. 

Rochling-Rodenhauser  furnaces  are  also  built  for  three-phase 
currents. 


CHAPTER   XIV 

THE   FIXATION   OP   ATMOSPHERIC   NITROGEN 

I.    INTRODUCTION 

NITROGEN,  though  chemically  an  inert  element,  is  of  great 
importance  to  plant  and  animal  life.  It  forms  80  per  cent  by 
volume  of  the  atmosphere,  but  it  has  been  impossible  until 
recently  to  get  atmospheric  nitrogen  in  a  combined  state  for 
use  in  fertilization  or  in  the  chemical  industries.  This  was  a 
problem  of  the  greatest  importance,  as  the  nitrogen  removed 
from  the  soil  by  crops  must  be  replaced  either  by  adding  it 
in  the  form  of  some  nitrogen  compound  or  by  raising  a  crop, 
such  as  clover,  that  assimilates  the  nitrogen  of  the  air  by  means 
of  a  certain  kind  of  bacteroid  existing  on  the  root  of  the  plant. 
Consequently,  Chili  saltpeter  is  used  in  large  quantities  for  fer- 
tilization, but  as  this  supply  is  not  expected  to  last  later  than 
1940,1  the  discovery  of  some  other  means  of  supplying  the 
demand  became  imperative. 

At  present  there  are  three  different  methods  in  operation 
of  combining  atmospheric  nitrogen.  The  first  method  con- 
sists in  heating  calcium  carbide  in  pure  dry  nitrogen  to  about 
1000°  C.,  whereby  nitrogen  is  absorbed,  forming  calcium  cyana- 
mide,  according  to  the  reversible  reaction  : 

CaC2  +  N±CaCN   +  C. 


The  second  method  consists  in  oxidizing  nitrogen  to  nitric 
oxide  in  the  electric  arc  and  absorbing  the  oxide  in  water  or  in 
an  alkaline  solution,  and  the  third  and  most  recent  method  is 
the  direct  synthesis  of  ammonia  from  its  elements. 

1  Edstrom,  Trans.  Am.  Electrochem.  Soc.  6,  17,  (1904). 
265 


266  APPLIED  ELECTROCHEMISTRY 

2.   ABSORPTION  BY  CALCIUM  CARBIDE 

According  to  Moissan,  pure  carbide  is  unaffected  by  nitro- 
gen at  1200°  C.1  The  discovery  that  nitrogen  is  absorbed  by 
commercial  calcium  carbide  and  barium  carbide  was  patented 
in  1895  by  Adolph  Frank  and  N.  Caro.2  In  the  case  of  barium 
carbide  30  per  cent  forms  cyanide  in  place  of  cyanamide,3  while 
in  the  case  of  calcium  only  a  trace  of  cyanide  is  formed. 

Since  1895  this  reaction  has  been  the  subject  of  a  number  of 
investigations.  With  regard  to  the  temperature  required,  it 
has  been  shown  that  finely  powdered  carbide  must  be  heated 
to  from  1000°  to  1100°  C.  to  bring  about  complete  transforma- 
tion to  cyanide.  At  800°  to  900°  some  nitrogen  is  absorbed, 
but  the  reaction  ceases  before  all  the  carbide  is  used  up.4  By 
the  addition  of  other  calcium  salts,  such  as  calcium  chloride,  or, 
to  a  less  extent,  calcium  fluoride,  complete  nitrification  can  be 
produced  at  700°  to  800°  C.5  That  the  commercial  carbide 
can  be  completely  nitrified  at  1100°  is  due  to  the  presence 
of  calcium  oxide.6  Commercial  calcium  carbide  containing  75 
to  80  per  cent  carbide  can  be  made  to  take  up  85  to  90  per 
cent  of  the  theoretical  amount  of  nitrogen,  forming  a  black 
mass  of  calcium  cyanamide,  lime,  and  carbon  containing  20  to 
23.5  per  cent  of  nitrogen.3  Pure  calcium  cyanamide  contains 
35  per  cent  nitrogen.  The  reaction  by  which  it  is  made  is 
accompanied  by  a  large  evolution  of  heat,  which  of  course 
is  advantageous  in  its  manufacture.  According  to  Caro,  this 
heat  is  sufficient  to  cause  the  reaction  to  proceed  of  itself  when 
once  started.7 

The  system  consisting  of  calcium  carbide,  calcium  cyanamide, 
carbon, .and  nitrogen,  is  monovariant,  that  is,  for  every  tem- 
perature there  is  a  corresponding  pressure  of  the  nitrogen  at 
which  equilibrium  exists.  This  equilibrium  has  been  meas- 

1  C.  R.  118,  501,  (1894).  2  Frank,  Z.  f.  angew.  Ch.  19,  835,  (1906). 

8  Erlwein,  Z.  f.  angew.  Ch.  p.  533,  (1903). 

4  Foerster  and  Jacoby,  Z.  f.  Elektroch.  15,  820,  (1909). 

5  Bredig,  Z.  f.  Elektroch.  13,  69,  (1907). 

6  Foerster  and  Jacoby,  Z.  f.  Elektroch.  13,  101,  (1907). 
*  N.  Caro,  Z.  f.  angew.  Ch.  22,  1178,  (1909). 


THE    FIXATION   OF  ATMOSPHERIC   NITROGEN 


267 


ured  between  1050°  C.  and  1450°  C.,  and  the  results  are  given 
in  the  plot  in  Figure  11 5. 8  If  the  initial  pressure  of  nitrogen 
lies  in  the  region  above  the  line,  absorption  of  nitrogen  takes 
place,  while  if  below,  any  calcium  cyanamide  present  would 


50 


40 


30 


20 


10 


4B 


1000 


1100 


1400 


1500 


1200  1300 

v  TEMPERATURE 

FIG.  115.  —  Plot  showing  pressures  and  temperatures  at  which  equilibrium  of  the 
reaction  CaC2+N2^:CaCN2  + C  exists.  Pressures  are  in  centimeters  of  mer- 
cury ;  temperatures  in  centigrade  degrees. 

decompose  until  the  nitrogen  produced  brings  the  pressure  up 
to  that  corresponding  to  equilibrium,  or  until  all  of  the  cyan- 
amide  is  used  up. 

The  velocity  of  absorption  of  nitrogen  is  proportional  to  its 
pressure,9  assuming  other  conditions  constant.  At  a  constant 

8  Thompson  and  Lombard,  Proc.  Am.  Acad.  46,  247,  (1910)  ;  Met.  and  Chem. 
Eng.  8,  617,  (1910).  During  proof  reading  the  experiments  of  Le  Blanc  and 
Eschmann,  with  results  different  from  those  above,  appeared  ;  see  Z.  f.  Elek- 
troch.  17,  20,  (1911).  They  find  that  the  pressure  depends  on  the  nitrogen  con- 
tent of  the  solid  phase  as  well  as  on  the  temperature. 

»  Bredig,  Fraenkel,  and  Wilke,  Z.  f.  Elektroch.  13,  605,  (1907). 


268  APPLIED   ELECTROCHEMISTRY 

temperature,  with  a  constant  surface  of  carbide  exposed,  and 
a  given  amount  of  nitrogen  in  a  given  volume,  this  law  is 
expressed  by  the  differential  equation  : 


where  p  is  the  pressure,  t  the  temperature,  and  k  is  a  constant. 
Integrated  this  becomes 


0.43  1         Pi 

where  p2  and  pl  are  the  pressures  at  the  beginning  and  end 
respectively  of  the  time  interval  t. 

Calcium  cyanamide  acts  in  some  cases  as  the  calcium  salt  of 
cyanamide  :  Ca  =  N  —  C  s  N,  and  in  others  as  the  calcium  salt 
of  the  diimide 


With  superheated  steam  the  nitrogen  is  changed  to  ammonia 
according  to  the  reaction2 

CaCN2  +  3  H20  =  CaCO3  +  2  NH3 

with  a  yield  99  per  cent.10  Dicyandiamid,  a  compound  con- 
taining 66  per  cent  nitrogen,  can  be  made  by  treating  calcium 
cyanamide  with  water.  It  has  the  appearance  of  ammonium 
chloride,  and  is  probably  formed  by  the  following  reaction  : 

2  CaCN2  +  4  H20  =  2  Ca(OH)2  +  (CNNH2)2.n 

Calcium  cyanide  can  be  made  from  technical  calcium  cyana- 
mide by  melting  with  a  suitable  flux,  such  as  sodium  chloride, 
according  to  the  following  reversible  reaction  : 


This  use  of  calcium  cyanamide  is  second  in  importance  only  to 
its  direct  application  as  a  fertilizer.2 

According  to  Frank2  one  horse  power  year  can  produce 
enough  carbide  to  absorb  772  kilograms  of  nitrogen,  though 
the  value  actually  realized  amounts  to  only  300  to  330  kilo- 

10  Erlwein,  Z.  f.  Elektroch.  12,  551,  (1906). 

11  Z.  f.  angew.  Ch.  p.  520,  (1903). 


THE    FIXATION   OF  ATMOSPHERIC    NITROGEN  269 

grams.  According  to  a  later  statement  by  Caro,7  3  horse  power 
years  is  more  than  sufficient  to  absorb  one  metric  ton  of  nitro- 
gen, including  the  manufacture  of  the  carbide  and  all  the  other 
power  required  in  the  factory  for  the  grinding  and  moving 
apparatus,  the  Linde  machines  for  liquefying  air,  and  so  forth. 
Thus  a  factory  with  12,000  horse  power  produces  yearly  20,000 
metric  tons  of  calcium  cyanamide  containing  20  per  cent  nitro- 
gen, corresponding  to  4000  metric  tons  of  nitrogen.  It  is  in- 
teresting to  compare  these  data  with  the  power  required  to 
produce  the  corresponding  amount  of  calcium  carbide.  An 
average  yield  of  carbide  has  been  shown  above  to  be  5.5  kilos 
of  80  per  cent  carbide  per  kilowatt  day,  corresponding  to  1500 
kilos  per  horse  power  year.  376  kilograms  of  nitrogen  would 
have  to  be  absorbed  by  this  amount  of  carbide  in  order  that  the 
product  should  contain  20  per  cent  nitrogen.  This  is  a  little 
above  the  value  300  to  330  actually  obtained  as  given  by  Frank. 
If  the  statement  of  Caro  is  correct,  and  carbide  is  produced  with 
the  efficiency  assumed  above,  it  means  that  90  per  cent  of  the 
power  in  a  cyanamide  factory  is  used  for  producing  the  carbide 
alone. 

Nitrogen  is  obtained  by  the  Linde  process  or  by  removing 
the  oxygen  with  hot  copper.  It  must  be  free  from  oxygen,  for 
this  would  produce  carbon  monoxide,  which  decomposes  both 
carbide  and  cyanamide.7  Caro  states  that  moisture  must  be  also 
absent,  though  Bredig,  Fraenkel,  and  Wilke's9  experiments 
showed  that  when  the  nitrogen  was  saturated  with  water  vapor 
at  22°,  a  little  more  nitrogen  was  absorbed  than  when  dry. 

Besides  lime  and  carbon,  there  are  impurities  in  technical 
cyanamide,  consisting  of  nitrogen  compounds,  such  as  urea, 
guanidine,  and  calcium  carbamate.  In  fresh  samples  these 
impurities  are  small  in  quantity,  but  increase  on  standing  or 
by  the  presence  of  water  vapor.  All  of  these  substances  are 
easily  assimilated  by  plants.7 

The  manufacture  of  calcium  cyanamide  was  begun  on  a  large 
scale  in  1905  at  Piano  d'Orta,  Italy,10  and  in  1908  there  were 
11  factories  in  Europe  making  this  substance.12  Norway  and 
i2Min.  Ind.  17,  105,  (1908). 


270  APPLIED   ELECTROCHEMISTRY 

Sweden  are  unusually  favorable  localities  for  the  nitrogen 
industry  on  account  of  the  large  amount  of  cheap  water  power. 
Recent  estimates  on  power  in  these  countries  are  as  follows :  13 


AVAILABLE 

DEVELOPED 

Sweden     

4,000,000  h.  p. 

400,000  h.  p 

Norway    . 

5  000  000  h.  p. 

500  000  h  p 

The  figures  under  "  developed  "  refer  to  plants  in  operation  or 
under  construction.  There  is  a  20,000  horse  power  plant  for 
the  production  of  cyanamide  and  calcium  carbide  at  Odda, 
Norway,  having  a  capacity  of  32,000  short  tons  of  carbide  and 
12,500  tons  of  cyanamide  per  year.  The  nitrogen,  which  must 
not  contain  over  0.4  per  cent  oxygen,  is  obtained  by  the  Linde 
process.  The  furnaces  in  which  the  carbide  is  heated  with 
nitrogen  are  charged  with  about  700  pounds  and  produce  2000 
pounds  of  cyanamide  containing  20  per  cent  nitrogen  per  week. 
In  1909  this  industry  was  introduced  on  this  side  of  the 
Atlantic  by  the  American  Cyanamide  Company,  which  owns 
the  exclusive  rights  for  manufacturing  nitrolime  in  this  country. 
A  factory  is  now  in  operation  at  Niagara  Falls,  Ontario.14  The 
product  is  to  contain  12  to  15  per  cent  nitrogen,  10  per  cent 
carbon,  and  25  per  cent  calcium  sulphate.  Free  lime  is  to  be 
eliminated  as  is  demanded  by  American  trade. 

3.    THE  OXIDATION  OF  NITROGEN 

Priestley l  was  the  first  to  observe  that  electric  sparks  in  air 
produced  an  acid,  though  he  mistook  it  for  carbonic  acid. 
Later  Cavendish2  repeated  the  experiments  and  showed  the 
true  nature  of  the  acid  produced,  which  is  now  known  to  be  a 
mixture  of  nitrous  and  nitric  acids.  From  the  time  of  Caven- 

13  Electrochem.  and  Met.  Ind.  7,  212  and  360,  (1909). 

14  Met.  and  Chem.  Eng.  8,  227,  (1910). 

1  Experiments  and  Observations  on  Different  Kinds  of  Air,  4,  286.  Preface 
dated  1779.  Also  Ostwald,  Elektrocheinie,  p.  11. 

a  Phil.  Trans.  75,  372-384,  (1797).    Also  Alembic  Club  Reprints,  No.  3,  p.  39. 


THE    FIXATION    OF   ATMOSPHERIC    NITROGEN 


271 


dish  until  within  the  last  twenty  years  nothing  of  importance 
was  done  toward  explaining  this  phenomenon.  Since  1890, 
however,  it  has  received  considerable  attention,  so  that  now, 
principally  due  to  the  work  of  Nernst  and  Haber,  the  conditions 
under  which  the  reaction  N2  +  O2  ^  2  NO  takes  place  are  well 
known. 

Nernst  and  his  assistants  have  measured  the  thermal  equilib- 
rium concentrations  of  nitrogen,  oxygen,  and  nitric  oxide  at 
different  temperatures  with  the  results  in  Table  32.3 

TABLE  32 
Per  cent  by  Volume  of  Nitric  Oxide  in  the  Equilibrium  Mixture  formed  from  Air 


DEGREES  ABSOLUTE 

PER  CENT 

NO 

OBSERVER 

1811  

Observed 

0.37 

Computed 

0.35 

Nernst 

1877  

0.42 

0.43 

Jellinek 

2023  

0.52  to  0.80 

0.64 

Jellinek 

2033  

0.64 

0.67 

Nernst 

2195  

0.97 

0.98 

Nernst 

2580  

2.05 

2.02 

Nernst-Finckh 

2675  

2.23 

2.35 

Nernst-Finckh 

The  values  in  the  third  column  were  computed  by  the  Van't 
Hoff  equation,  with  Berthelot's  value  of  —  21,600  calories  for 
the  heat  of  the  reaction.  These  experiments  show  that  at  the 
temperatures  given  the  velocity  of  decomposition  is  so  low  that 
the  gas  can  be  cooled  without  decomposition  of  the  nitric  oxide 
already  formed. 

The  free  energy  of  the  reaction  is  given  by  the  equation  4 


=  Q  -ET  log- 


+  2.45  T, 


in  which  Q  =  —  21,600  calories.  By  means  of  this  equation 
the  per  cent  of  nitric  oxide  corresponding  to  the  equilibrium 
at  any  temperature  can  be  computed  by  placing  the  right-hand 

»  Z.  f.  anorg.  Ch.  49,  213,  (1906). 

*  Haber,  Thermodynamics  of  Technical  Gas  Reactions,  p.  105,  (1908). 


272 


APPLIED    ELECTROCHEMISTRY 


side  equal  to  zero,  which  is  the  equilibrium  condition.  The 
experiments  of  Finckh  were  carried  out  by  exploding  air  mixed 
with  detonating  gas ;  the  others  by  drawing  air  through  plati- 
num or  iridium  tubes  heated  electrically.  The  good  agreement 
between  the  calculated  and  observed  values  shows  that  at  least 
in  these  experiments  the  nitric  oxide  formed  is  due  only  to  the 
high  temperature,  as  the  concentration  is  that  required  by 
thermodynamics. 

This  reaction  is  bimolecular  between  650°  C.  and  1750°  C.,5 
that  is  to  say,  it  should  be  written  N2  +  O2  =  2  NO.  Le  Blanc 
and  Niiranen,  however,  have  found  that  above  3000°  C.  the 
reaction  is  monomolecular.6  Tables  33  and  34  give  the  veloci- 
ties of  the  reaction  in  both  directions  at  different  temperatures.6 

TABLE  33 

Time  in  Minutes  necessary  to  decompose  Pure  Nitric  Oxide  at  Atmospheric  Pres- 
sure, Half  into  Nitrogen  and  Oxygen 


DEGREES  ABSOLUTE 

TIME  IN  MINUTES 

DEGREES  ABSOLUTE 

TIME  IN  MINUTES 

900 

7.35     103 

2100 

1.21     10-3 

1100 

5.80     102 

2300 

8.40     10-5 

1300 

4.43     101 

2500 

5.76     10-6 

1500 

3.30 

2700 

3.92     10-7 

1700 

2.47     10-1 

2900 

3.35     10~8 

1900 

1.47     lO-2 

3100 

2.25     10-9 

TABLE  34 
Time  required  to  produce  from  Air  One  Half  the  Possible  Amount  of  Nitric  Oxide 


DEGREES  ABSOLUTE 

TIME  IN  MINUTES 

DEGREES  ABSOLUTE 

TIME  IN  MINUTES 

1500 

1.81  108 

2500 

1.77   10~4 

1700 

5.90  101 

2700 

8.75  10-6 

1900 

2.08 

2900 

5.75  10-7 

2100 

8.43  10-2 

3100 

3.10  10-8 

2300 

3.75  10-8 

5  Jellinek,  Z.  f.  anorg.  Ch.  49,  229,  (1906). 

6  Z.  f.  Elektroch.  13,  303,  (1907). 


THE    FIXATION   OF  ATMOSPHERIC   NITROGEN 


273 


From  these  results  it  would  appear  that  the  best  yield  of 
nitric  oxide  would  be  obtained  by  heating  the  gas  to  the 
highest  temperature  from  which  it  could  be  chilled  so  suddenly 
that  decomposition  would  not  take  place.  It  has  been  shown, 
however,  that  nitric  oxide  can  be  produced  by  the  silent  dis- 
charge of  electricity  where  there  is  very  little  elevation  of 
temperature.7  This  fact  suggested  to  Haber  and  Koenig8  the 
possibility  of  obtaining  better  yields  by  using  a  comparatively 
cool  arc,  which  could  be  realized  by  inclosing  it  in  a  tube 
surrounded  by  water.  Below  3000°  C.  any  oxide  produced  by 
the  impact  of  electrons  would  not  be  decomposed  rapidly  by 
the  heat  even  if  the  concentration  due  to  the  electrical  effect 
were  greater  than  that  due  to  the  thermal.  In  fact  they  found 
that  by  using  a  cooled  arc  and  by  reducing  the  pressure  to  the 
most  favorable  value  of  100  millimeters,  concentrations  of 
nitric  oxide  were  obtained  which  could  be  explained  thermally 
only  on  the  assumption  that  the  thermal  equilibrium  correspond- 
ing to  over  4000°  absolute  had  been  obtained  and  that  the  gas 
had  been  chilled  suddenly  enough  to  preserve  it.  Such  a  high 


TABLE  35 

Concentrations  of  Nitric  Oxide  obtained  at  100  mm.  Pressure  by  an  Arc  inclosed  in 

a  Cooled  Tube 


INITIAL  GAS  MIXTURE  IN 

THERMODYNAMICALLY  COM- 

PER CENT  BY  VOL. 

7>NO 

NO  CONTENT 

PUTED  TEMP.  ABS. 

i           i 

IN  PER  CENT 

_£)   O2  •  ft    N^2 

-y 

o, 

N, 

Haber 

Nernst 

20.9 

79.1 

0.284 

9.8 

4365 

4334 

48.9 

51.1 

0.337 

14.4 

4686 

4650 

44.4 

55.6 

0.337 

14.3 

4686 

4650 

75.0 

25.0 

0.357 

12.77 

4805 

4767 

81.7 

18.3 

0.397 

12.1 

5042 

5000 

7  Warburg  and  Leithauser,  Ann.  d.  Phys.   (4)  20,  743,  (1906),  and  23,  209, 
(1907). 

8  Z.  f.  Elektroch.  13,  725,  (1907). 


274  APPLIED   ELECTROCHEMISTRY 

temperature  in  their  arc  seemed  impossible ;  consequently  the 
oxide  must  have  been  produced  directly  by  the  impact  of  ions. 
Table  35  gives  the  concentrations  of  nitric  oxide  obtained  with 
the  temperature  corresponding,  on  the  improbable  assumption 
that  this  concentration  corresponds  to  a  thermal  and  not  to  an 
electrical  equilibrium.  The  temperatures  were  computed  both 
by  Haber's  formula  given  above  and  by  the  Van't  Hoff  formula 
as  used  by  Nernst. 

In  later  experiments  as  high  as  17.8  per  cent  nitric  oxide  was 
obtained.9  It  was  further  found  that  the  same  concentration 
is  obtained  under  similar  conditions  from  either  nitric  oxide 
or  from  air  and  oxygen,  showing  that  we  have  in  this  case 
an  electrical  equilibrium.  If  the  temperature  is  too  high,  the 
electrical  equilibrium  is  obliterated  by  the  thermal.  On  the 
other  hand,  the  electrical  energy  necessary  to  produce  ioniza- 
tion  increases  considerably  when  the  temperature  falls  below 
white  heat.  There  will  therefore  be  a  most  favorable  region 
of  temperature  within  which  the  nitric  oxide  produced  by  the 
impact  of  ions  will  not  be  decomposed  and  when  too  much 
electrical  energy  is  not  required  for  ionization.8  It  would, 
therefore,  seem  that  the  best  way  to  try  to  obtain  better  re- 
sults is  to  employ  a  cool  arc  rather  than  by  attempting  to  heat  to 
a  higher  temperature  and  chill  more  suddenly. 

The  energy  efficiency  was  not  determined  in  these  experi- 
ments. In  later  ones,10  with  a  cooled  arc,  the  efficiency,  when 
the  concentration  of  the  nitric  acid  obtained  was  3.4  per  cent, 
was  57  grams  of  nitric  acid  per  kilowatt  hour,  or  500  kilo- 
grams per  kilowatt  year  of  365  x  24  hours.  With  a  cooled 
arc  and  a  direct  current,  Holweg  and  Koenig n  obtained 
nitric  acid  at  a  concentration  of  2.5  per  cent  and  an  efficiency 
corresponding  to  80  grams  of  nitric  acid  per  kilowatt  hour, 
the  most  favorable  energy  efficiency  ever  reached.  Increas- 
ing the  pressure  above  atmospheric  does  not  increase  this 
efficiency.12 

»  Z.  f.  Elektroch.  14,  689,  (1908).  10  Z.  f.  Elektrock.  16,  795,  (1910). 

"  Z.  f.  Elektroch.  16,  809,  (1910). 
12  Haber  and  Holweg,  Z.  f.  Elektroch.  16,  810,  (1910).  * 


THE    FIXATION   OF   ATMOSPHERIC    NITROGEN 


275 


On  cooling  down,  the  colorless  nitric  oxide  changes  to  the 
brown  dioxide  of  nitrogen,  since  the  reversible  reaction 

NO  +  \ r  02  ^±  N02 

is  displaced  from  left  to  right  on  cooling. 

Table  36  shows  how  the  dissociation  of  nitrogen  dioxide  is 
affected  by  the  temperature  : 13 


TABLE  36 


DEGREES  CENTIGRADE 

PRESSURE  IN  CENTIMETERS 

PER  CENT  OF  NO2  DECOMPOSED 

130 

71.85 

184 

75.46 

5.0 

279 

73.72 

13.0 

494 

74.25 

56.5 

620 

76.00 

100.0 

It  will  be  interesting  to  compute  from  a  purely  thermal 
standpoint  the  energy  necessary  to  produce  nitric  acid  and  to 
compare  this  result  with  those  actually  found  by  different  ex- 
perimenters. Assuming  the  temperature  of  the  high  tension 
arc  to  be  4200°  C.,  the  calculation  is  as  follows.14  From  the 
equation  given  above  at  this  temperature 


=0.29, 


and  if  the  original  mixture  is  air,  the  final  composition  is : 

NO  O2  N2 

10  per  cent  16  per  cent  74  per  cent 

Ten  moles  of  nitric  oxide  with  air  and  water  yield  630  grams  of 
nitric  acid.  Therefore,  in  order  to  get  this  amount  of  acid, 
100  moles  must  be  heated  to  4200°  C.,  besides  which  10  x  21,600 
calories  must  be  supplied  for  the  reaction.  Assuming  the  spe- 

18  Nernst,  Theoretische  Chemie,  p.  455,  6th  ed.    See  also  Bodenstein  and  Kata- 
yama,  Z.  f.  Elektroch.  15,  244,  (1909). 

14  Haber,  Thermodynamics  of  Technical  Gas  Reactions,  p.  268. 


276  APPLIED   ELECTROCHEMISTRY 

cific  heat  of  the  permanent  gases  to  be  6.8  -f  0.0006  calories 
per  mole,  the  total  energy  will  be : 

100  (6.8  +  0.0006  x  4200)  4200  +  216,000  =  4,130,000  calories. 

This  corresponds  to  4.71  kilowatt  hours  for  630  grams  of  nitric 
acid,  or  134  grams  per  kilowatt  hour.  If  the  arc  were  1000° 
lower,  the  result  would  be  93.5  grams  per  kilowatt  hour. 

The  results  obtained  with  a  cooled  arc  are  not  due  to  ther- 
mal equilibrium,  and  of  course  have  no  relation  to  this  calcula- 
tion. Unless  special  precautions  were  taken  to  use  a  cooled 
arc,  the  results  may  be  assumed  to  be  due  to  thermal  and  not 
to  electrical  causes.  This  is  the  case  in  the  following  examples. 

Lord  Rayleigh 15  obtained  an  absorption  of  21  liters  an  hour 
with  0.8  kilowatt,  using  a  mixture  of  9  parts  of  air  and  11  of 
oxygen.  This  corresponds  to  46  grams  of  pure  nitric  acid  per 
kilowatt  hour,  assuming  the  gas  was  measured  at  20°  C.  and  at 
atmospheric  pressure.  McDougall  and  Howies  16  with  an  ar- 
rangement similar  to  that  of  Lord  Rayleigh  obtained  33.5  grams 
of  nitric  acid  per  kilowatt  hour.  McDougall  and  Howies  were 
the  first  to  make  a  small  experimental  plant  for  the  production 
of  nitric  acid  from  the  air.17  It  seems  not  to  have  got  beyond 
the  experimental  stage,  however. 

The  first18  attempt  to  carry  out  the  oxidation  of  nitrogen  on 
a  commercial  scale  was  that  of  the  Atmospheric  Products  Com- 
pany at  Niagara  Falls,  using  the  patents  of  Bradley  and  Love- 
joy.  Their  first  apparatus 19  was  similar  to  that  of  McDougall 
and  Howies  and  consisted  in  a  number  of  small  compartments 
in  which  an  arc  was  formed  between  electrodes  in  the  form  of  a 
hook  at  the  points  nearest  together,  as  shown  in  Figure  116.  The 
arc  then  ran  along  the  electrodes,  thereby  becoming  longer, 
until  it  went  out,  whereupon  the  arc  was  formed  again.  This 

i5  Journ.  Chem.  Soc.  71,  181,  (1897). 

,16  Memoirs  and  Proceedings  of  the  Manchester  Literary  and  Phil.  Soc.  (IV) 
44,  1900,  No.  13. 

17  Huber,  Zur  Stickstoff  Frage,  p.  41,  Bern,  (1908). 

18  Donath  and  Frenzel,  Die  Technische  Ausinetzung  des  Atmospharischen 
Stickstoffes,  p.  126,  (1907). 

»  U.  S.  Pat.  709,867,  (1902). 


THE    FIXATION    OF   ATMOSPHERIC    NITROGEN 


277 


arrangement  was  supplanted  by  a  single  apparatus,  shown  in 
Figures  117  and  118,  in  which  6900  arcs  were  formed  per 
second.20  This  consisted  in  an  iron  cylinder  5  feet  high,  4  feet 
in  diameter,  in  the  center  of  which  was  a  rotating  shaft  carry- 
ing a  series  of  radial  arms,  the  ends  of  which  were  tipped  with 


FIG.  116.  —  First  apparatus  of 
Bradley  aud  Lovejoy 


platinum.  Six  rows  of  23  inlet  wires  projected  through  the 
cylinder  and  terminated  in  a  platinum  hook.  As  the  radial 
arms  rotated,  their  platinum  tips  passed  the  hooks  on  the  inlet 
wires,  coming  within  one  millimeter  of  touching  at  the  nearest 
point.  An  arc  was  formed  which  was  drawn  out  from  4  to  6 
inches  before  going  out.  The  arms  were  so  arranged  that  the 

20  J.  W.  Richards,  Electroch.  Ind.  1,  20,  (1902)  ;  U.  S.  Pat.  709,868,  (1902). 


278 


APPLIED   ELECTROCHEMISTRY 


arcs  between  them  and  the  inlet  wires  were  formed  successively 
rather  than  simultaneously.  The  central  shaft  made  500  rota- 
tions per  minute.  Each  inlet  wire  had  in  series  with  it  an  in- 
duction coil  12  inches  long  and  5  inches  in  diameter,  wound 
with  very  fine  wire  and  immersed  in  oil.  The  self-induction  of 
the  coil  caused  the  spark  to  be  drawn  out  to  a  greater  length 
than  would  be  possible  without  induction.  A  direct  current 


FIG.  117.  —  Vertical  section  of  final 
apparatus  of  Bradley  and  Lovejoy 


generator  was  especially  designed  for  this  plant,  giving  8000 
volts  and  0.75  ampere.  Air  passed  in  at  the  rate  of  11.3  cubic 
meters  per  second  and  came  out  of  the  cylinder  containing  2.5 
per  cent  nitric  oxide.21  The  yield  is  said  to  have  been  one 
pound  of  acid  per  7  horse  power  hours,  or  87  grams  per  kilo- 
watt hour.  The  process  was  not  successful,  however,  and  the 
company  was  forced  to  give  up  the  experiments  in  1904. 
21  Haber,  Z.  f.  Elektroch.  9,  381,  (1903). 


THE    FIXATION    OF   ATMOSPHERIC    NITROGEN 


279 


Though  the  yield  compared  favorably  with  the  calculations 
given  above,  the .  apparatus  was  very  complicated  and  subject 
to  considerable  wear.  The  iron  drum  corroded  rapidly  in  spite 
of  the  inside  coating  of  asphalt  paint.18 

The  first  successful  process  for  oxidizing  nitrogen  on  a  com- 
mercial scale  is  that  of  Birkeland  and  Eyde.  A  factory  for 
carrying  it  out  was  started  at  Notodden,  Norway,  in  May,  1905. ^ 
The  high  voltage  flame  is  formed  between  two  electrodes  con- 
sisting of  water-cooled  copper  tubes  1.5  centimeters  in  diameter 


FIG.  118.  —  Horizontal  section  of  final  apparatus  of  Bradley  and  Lovejoy 

with  0.8  centimeter  between  the  ends.  An  alternating  current 
of  50  cycles  per  second  is  supplied  to  the  electrodes  at  5000 
volts.  In  order  to  spread  the  flame  over  a  large  area  an 
electromagnet  is  placed  at  right  angles  to  the  electrodes  so  that 
the  terminals  lie  between  the  poles  of  the  magnet.  The 
voltage  is  sufficiently  high  to  cause  the  flame  to  form  of  itself 
between  the  electrodes  at  their  nearest  points,  whereupon  the 
magnetic  field  causes  the  ends  of  the  flame  to  travel  along  the 
electrodes  until  the  current  is  reversed.  A  new  flame  is  then 
started  on  the  other  side  of  the  electrodes.  When  the  furnace 
22  Birkeland,  Trans.  Faraday  Soc.  2,  98,  (1906). 


280 


APPLIED   ELECTROCHEMISTRY 


is  running  properly  a  flame  is  formed  at  each  reversal  of  the 
current  every  ^  of  a  second,  though  if  the  distance  between 


FIG.  119.  —  Electric  disc  in  the  furnace  of  Birkeland  and  Eyde 

the  electrodes  is  too  short  or  the  magnetic  field  too  strong, 
several  hundred  flames  may  be  started  during  one  period.     The 

magnetic      field     is 

J  V      4000   to  5000   lines 

per  square  centi- 
meter at  the  center. 
The  result  of  this 
combination  is  an 
electric  disk  flame, 
as  shown  in  Figure 
119.  This  is  in- 
closed in  a  narrow 
iron  furnace  lined 
with  fire  brick,  form- 
ing a  chamber  from 
5  to  15  centimeters 
wide,  shown  in 
Figure  120.  Air 

120.  -  Vertical  section  of  furnace  of  Birkeland        I*8808     in      tlir°USh 

and  Eyde  the  walls  and  leaves 


THE    FIXATION    OF   ATMOSPHERIC    NITROGEN  281 

the  furnace  at  a  temperature  between  600°  and  700°  C.,  con- 
taining one  per  cent  of  nitric  oxide.  From  the  furnace  the 
gases  pass  through  a  steam  boiler  in  which  they  are  cooled 
to  200°  C.,  and  then  through  a  cooling  apparatus  in  which 
their  temperature  is  reduced  to  50°  C.  They  then  enter 
oxidation  chambers  with  acid  proof  lining,  where  the  reaction 
NO  +  $  O2  =  NO2  is  completed. 

The  next  step  is  to  absorb  the  nitrogen  dioxide.  This  is 
done  in  two  sets  of  five  stone  towers  whose  inside  dimensions 
are  2  x  2  x  10  meters.  The  first  four  towers  are  filled  with 
broken  quartz  over  which  water  trickles.  The  fifth  tower  is 
filled  with  brick,  and  the  absorbing  liquid  is  milk  of  lime,  giving 
a  mixture  of  calcium  nitrate  and  nitrite.  Nitric  acid  is 
formed  in  the  first  four  towers  with  concentrations  as  follows  : 

FIRST  SECOND  THIRD  FOURTH 

50  %  HXO3  25  %  HNO3  15%  HNO3  5%  HNO3 

The  liquid  from  the  fourth  tower  is  raised  by  compressed  air 
to  the  top  of  the  third,  that  from  the  third  to  the  top  of  the 
second,  and  so  on  until  fifty  per  cent  nitric  acid  is  formed. 
Some  of  this  acid  is  used  to  decompose  the  nitrate-nitrite 
mixture  from  the  fifth  tower.  The  nitric  oxide  thereby 
evolved  is  sent  into  the  absorbing  system  again.  About  97 
per  cent  of  the  entire  quantity  of  nitrous  gases  passed  through 
the  absorbing  system  is  absorbed.23  The  resulting  solution  of 
calcium  nitrate  and  the  rest  of  the  stored-up  acid  is  treated  in 
another  set  of  tanks  with  lime,  producing  neutral  calcium 
nitrate.  This  is  evaporated  in  iron  by  the  steam  from  the 
boilers  above  mentioned  till  a  boiling  point  of  145°  C.  is  reached, 
corresponding  to  75  or  80  per  cent  nitrate  and  containing  13.5 
per  cent  of  nitrogen.  This  is  poured  into  iron  drums  of  200 
liters  capacity,  where  it  solidifies.  Another  method  is  to 
crystallize  from  a  boiling  point  of  120°  C.  This  yields  calcium 
nitrate  with  four  molecules  of  water. 

In  1906  at  the  Notodden  Saltpeter  Manufactory  there  were 
three  500-kilowatt  furnaces  in  constant  activity.     The  volume 
28  Eyde,  Electrochem.  and  Met.  Ind.  7,  304,  (1909). 


282  APPLIED   ELECTROCHEMISTRY 

of  air  treated  was  75000  liters  per  minute.  The  yield  was 
about  500  kilograms  of  pure  nitric  acid  per  kilowatt  year,  or 
57  grams  per  kilowatt  hour. 

In  place  of  the  smaller  furnaces  those  now  used  absorb  1600 
kilowatts,  of  which  35  are  now  in  operation  at  Notodden,  8  in 
series.  The  disk  flame  has  a  diameter  of  2  meters  and  a 
thickness  of  10  centimeters.24 

During  the  year  1908  the  profits  of  the  Notodden  factory  were 
25  per  cent  of  the  total  receipts,  amounting  to  500,000  krone, 
or  $  135,000. M  The  company  using  the  Birkeland-Eyde  process 
has  combined  with  the  Badische  Anilin  und  Sodafabrik,  which 
has  developed  another  furnace,  described  below,  so  that  the  re- 
sults of  a  factory  under  construction  at  Notodden  in  1909  will 
decide  which  furnace  will  be  the  one  for  the  final  large  plant.25 
Up  to  February,  1909, 16,000,000  had  been  invested  at  Notodden 
and  Svalgfos  and  on  the  rivers  Rjukan  and  Vamma.  By  the 
end  of  1910  these  plants  will  be  completed  and  the  investment 
will  amount  to  fl^OOO^OO.25 

The  furnace  of  the  Badische  Anilin  und  Sodafabrik  of 
Ludwigshafen,  Germany,  was  invented  in  1905  by  Schonherr 
and  Hessberger.26  An  alternating  current  arc  is  very  easily 
extinguished,  especially  if  air  is  blown  across  it.  The  principle 
underlying  this  furnace  is  that  an  alternating  current  arc  loses 
its  unstable  character  and  becomes  as  quiet  as  a  candle  if  a  cur- 
rent of  air  is  passed  around  it  in  a  helical  path.  With  this 
method  of  air  circulation  the  arc  may  be  included  in  a  metallic 
tube  without  risk  of  its  coming  in  contact  with  the  sides  of  the 
tube.  A  cross  section  of  the  apparatus  is  shown  in  Figure  121. 
It  consists  of  a  number  of  concentric  vertical  iron  tubes.  The 
electrode  at  the  bottom  is  an  iron  rod  adjustable  within  a  water- 
cooled  copper  cylinder.  The  iron  is  slowly  eaten  away,  and  is 
fed  in  at  about  the  rate  of  one  electrode  in  three  months.  The 
electrode  Z  is  for  starting  the  arc  by  bringing  it  in  contact  with 

24  Birkeland,  Electrochem.  and  Met.  Ind.  7,  305,  (1909). 

25  Eyde,  Z.  f.  Elektroch,  15,  146,  (1909). 

2^  Electrochem.  and  Met.  Ind.  7,  245,  (1909) ;  Trans.  Am.  Electrochem.  Soc. 
16,  131,  (1909). 


FIXATION  OF  ATMOSPHERIC   NITROGEN      283 

E.     There  is  of  course  an  induction  coil 

in  series  with  the  arc  to  make  it  steady 

\         and  prevent  the  current  from  being  too 

large  on  starting.     When   Z  is  drawn 

back  the  arc  is  formed  between  E  and 

«*        the  walls   of   the  tube.      The  air  then 

|        drives   it   up   along    the    tube   until    it 

|         reaches  the  other  water-cooled  end,  JT, 

within  which  the  arc  terminates.      6rr 

2  6r2,  and  6r3  are  peep  holes  for  observing 
!  §,     the  ends  of  the  arc.     In  the  600  horse 
1  .-§     power  furnaces  at   Kristianssand,   Nor- 
§  bj>     way,  the  arc   is  5  meters  long,  and  7 
8 |     meters   in   the    1000   horse   power   fur- 
H  '§     naces.      The   circulation   of   the   air    is 
g       evident  from  the  figure. 

The  plant  at  Kristianssand,  the  fur- 

3  nace  room  of  which  is  shown  in  Figure 
122,   has    been    in    operation    since   the 
autumn  of  1907.     Three-phase  currents 

4  are  used,  and  the  furnaces  are  connected 
in  star.    The  power  factor  varies  between 

H  0.93  and  0.96.  It  is  estimated  that  3  per 
cent  of  the  power  is  used  in  the  formation 
of  nitric  oxide,  40  per  cent  is  recovered 
in  the  form  of  hot  water,  17  per  cent  is 
lost  by  radiation,  30  per  cent  is  used  in 
the  steam  boiler,  and  10  per  cent  is 
removed  by  water  cooling  after  the 
erases  have  passed  the  steam  boiler. 

O  ±T 

The  nitric  oxide  is  absorbed  by  milk  of 
lime.  The  final  product  is  calcium 
nitrite  containing  18  per  cent  nitrogen. 
The  yield  per  kilowatt  hour  is  not  given. 
A  third  process  for  the  fixation  of  at- 
mospheric nitrogen,  invented  by  H.  and 
G.  Pauling,  is  carried  out  near  Inns- 


284 


APPLIED   ELECTROCHEMISTRY 


bruck,  Tirol,  by  the  "  Salpetersaure-Industrie-Gesellschaft."27 
The  arcs  are  produced  between  curved  electrodes,  as  shown  in 
Figure  123.  The  arc  is  lighted  where  the  electrodes  are  near- 
est together,  is  blown  upwards  by  the  hot  air  rising  between 


FIG.  122.  — Furnace  room  at  Kristianssaud 

the  electrodes,  and  is  broken  every  half  period  of  the  alternating 
current.  Another  arc  is  then  formed,  and  so  on.  In  Figure  123 
c  represents  two  thin  adjustable  blades  for  starting  the  arc. 
Air  is  blown  in  through  the  tube  e.  The  electrodes  are  iron 
pipes,  water-cooled  and  separated  by  about  4  centimeters  at 
,27  Electrochem.  and  Met.  Ind.  7,  430,  (1909). 


THE    FIXATION   OF   ATMOSPHERIC    NITROGEN 


285 


their  nearest  point.  Their  life  is  about  200  hours.  With  a 
400  kilowatt  furnace  of  4000  volts  the  length  of  the  flame  is 
about  one  meter.  Cooling  is  produced  by  passing  cold  air  into 
the  upper  part  of  the  flame  from  the  side.  The  concentration 
of  the  nitric  oxide  is  about  1.5  per  cent.  The  furnaces  used 
have  two  arcs  in  series. 
Six  hundred  cubic 
meters  of  air  per  hour 
pass  through  the  fur- 
nace, excluding  the 
cooling  air.  The 
yield  is  60  grams  of 
nitric  acid  per  kilo- 
watt hour.  At  pres- 

*  FIG.  123.  —  Electrodes  in  lurnace  of 

ent  there  are  24  fur-  H.  and  G.  Pauling 

naces  in  operation  at 

Innsbruck,  having   a  capacity   of   15,000   horse   power.     The 

products  are  nitric  acid  and  sodium  nitrite.     Two  other  plants 

for  carrying  out  this  process,  each  of  10,000  horse  power,  are 

in  course  of  erection,  one  in  southern  France  and  the  other  in 

northern  Italy. 

A  number  of  other  furnaces  for  the  oxidation  of  nitrogen 
have  been  invented,  but  their  descriptions  are  omitted  here 
because  they  are  not  in  operation  on  a  commercial  scale. 


4.   THE  SYNTHESIS  OF  AMMONIA 

The  third  method  of  fixing  nitrogen,  that  has  just  recently 
been  taken  up  by  the  Badische  Anilin  und  Sodafabrik,1  is  to 
make  it  combine  directly  with  hydrogen  to  form  ammonia,  ac- 
cording to  the  reversible  reaction  : 


This  reaction  takes  place  from  left  to  right  with  the  evolution 
of  about  12,000  calories,2  so  that  the  quantity  of  ammonia  gas  in 
the  equilibrium  mixture  decreases  as  the  temperature  rises. 

1  Haber,  Z.  f.  Elektroch.  16,  242,  (1910). 

2  Landolt  and  Bernstein's  Tables,  3d  ed.  p.  427. 


286 


APPLIED   ELECTROCHEMISTRY 


The  velocity  of  the  reaction,  on  the  other  hand,  of  course  in- 
creases with  the  temperature,  but  does  not  reach  a  value  that 
adjusts  the  equilibrium  rapidly  below  a  temperature  of  750°  C.3 
The  composition  of  the  equilibrium  mixtures  for  different  tem- 
peratures and  two  different  pressures,  when  the  free  hydrogen 
and  nitrogen  are  present  in  the  same  proportion  as  in  ammonia, 
is  given  in  Table  37.4 

TABLE  37 


DEGREES 

PRESSURE  IN 

VOL.  PER  CENT 

PRESSURE  IN 

VOL.  PER  CENT 

CENTIGRADE 

ATMOSPHERES 

NH, 

ATMOSPHERES 

NH3 

700 

30 

0.654 

1 

0.0221 

801 

30 

0.344 

1 

0.0116 

901 

30 

0.207 

1 

0.00692 

974 

30 

0.144  to  0.152 

-      1 

0.0048  to  0.0051 

It  is  evident  from  this  table  that  unless  some  catalytic  agent 
can  be  found  that  would  give  the  reaction  high  velocity  at  a 
temperature  considerably  below  750°,  very  little  ammonia  could 
be  obtained  at  atmospheric  pressure.  Since,  however,  there  is 
a  decrease  in  volume  when  ammonia  is  formed  from  an  equiva- 
lent amount  of  nitrogen  and  hydrogen,  there  must  be  an  in- 
crease in  the  relative  amount  of  ammonia  in  an  equilibrium 
mixture  when  the  pressure  is  increased.  It  is  evident  from 
the  table  that  the  volume  per  cent  of  ammonia  in  such  a  mixture 
is  directly  proportional  to  the  pressure,  as  long  as  the  relative 
amounts  of  free  hydrogen  and  nitrogen  are  kept  constant. 

Jost5  has  obtained  somewhat  lower  values  for  the  amount 
of  ammonia  in  the  equilibrium  mixture.  Table  38  gives  his 
results  obtained  at  a  total  pressure  of  one  atmosphere,  and  those 
of  Haber  taken  from  the  table  above  for  comparison. 

Haber's  results  at  one  atmosphere  are  in  good  agreement 
with  the  values  calculated  from  his  results  at  30  atmospheres, 
and  therefore  are  more  reliable  than  Jost's. 

8  Haber,  Thermodynamics  of  Technical  Gas  Reactions,  p.  202,  (1908). 
*  Haber  and  Le  Rossignol,  Z.  f.  Elektroch.  14,  193,  (1908). 
5  Z.  f.  Elektroch.  14,  373,  (1908). 


THE    FIXATION    OF   ATMOSPHERIC    NITROGEN 
TABLE  38 


287 


VOLUME  PER  CENT  NH8 

T*                 r* 

Haber 

Jost 

700 

0.0221 

0.018 

800 

0.0116 

0.0090 

900 

0.0069 

0.0050 

974 

0.0048  to  0.0051 

0.0035 

Haber  lias  subsequently  developed  this  process  further  and 
showed  in  a  lecture 1  a  small  apparatus  working  at  185  atmos- 
pheres that  produced  hourly  90  grams  of  liquid  ammonia.  In 
the  earlier  experiments  finely  divided  iron  on  asbestos  was  used 
as  a  catalyzer,  but  in  these  later  experiments,  uranium  was 
substituted  for  iron.  This  method  is  said  to  require  compara- 
tively little  power,  and  will  therefore  not  be  confined  to  places 
where  cheap  water  power  is  available.  No  numerical  values  of 
the  efficiency  of  this  method,  however,  are  given. 

5.    CONCLUSION 

Having  described  the  three  general  methods  of  fixing  atmos- 
pheric nitrogen  now  in  operation,  it  will  be  interesting  to  com- 
pare the  actual  amounts  of  nitrogen  fixed  for  a  given  amount 
of  power  by  the  three  methods.  This  is  possible  only  for  the 
absorption  by  carbide  and  the  direct  oxidation. 

Since  12,000  horse  power  or  8850  kilowatts  can  fix  4,000,000 
kilograms  of  nitrogen l  per  year  as  calcium  cyanamide,  one  kilo- 
watt hour  corresponds  to  51.6  grams  of  nitrogen.  The  yield 
by  the  Birkeland-Eyde  process  is  about  57.1  grams  of  pure 
nitric  acid  per  kilowatt  hour,2  corresponding  to  12.7  grams  of 
nitrogen.  The  cyanamide  process  therefore  fixes  about  four 
times  as  much  nitrogen  as  the  direct  oxidation  for  the  same  ex- 
penditure of  power. 

i  Frank,  Z.  f.  angew.  Ch.  19,  835,  (1906). 

2Birkeland,  Trans.  Faraday  Soc.  2,  98,  (1906);  Haber,  Z.  f.  Elektroch.  10, 
551,  (1906). 


CHAPTER   XV 

THE  PRODUCTION   OF   OZONE 

1.    GENERAL  DISCUSSION 

IN  1785  Van  Marum  observed  that  oxygen  through  which 
an  electric  spark  had  passed  had  a  peculiar  odor,  and  that  it  at 
once  tarnished  a  bright  surface  of  mercury.1  Nothing  was 
done  to  throw  light  on  this  phenomenon  until  1840,  when  it 
was  investigated  by  Schonbein.  He  had  observed  for  a  num- 
ber of  years  previously  that  during  the  electrolysis  of  aqueous 
solutions  an  odor  is  produced  in  the  gas  evolved  at  the  anode 
similar  to  that  resulting  from  the  discharge  of  electricity  from 
points.2  He  described  a  number  of  the  properties  of  this  sub- 
stance, and  suggested  the  name  ozone,  from  6'£&>i>,  meaning 
smelling.  For  many  years  the  chemical  nature  of  this  oxidiz- 
ing principle  was  unknown,  but  it  was  found  eventually,  after 
a  great  number  of  investigations,  to  be  simply  condensed 
oxygen  with  the  formula  O3. 

The  formation  of  ozone  from  oxygen  is  an  endothermic 
reaction.  The  heat  absorbed  in  the  production  of  one  mole 
of  ozone,  as  determined  by  different  investigators,  is  given 
in  the  following  table  : 3 

Berthelot,  indirect,  1876 29,800  calories 

Mulder  and  v.  d.  Meulen,  indirect,  1883  .     .     .  33,700  calories 

v.  d.  Meulen,  indirect,  1882 32,800  calories 

v.  d.  Meulen,  direct,  1883 36,500  calories 

Jahn,  direct,  1908      . 34,100  calories 

1  Roscoe  and  Schorlemmer,  Treatise  on  Chemistry,  1,  256,  (1905). 

2  Pogg.  Ann.  50,  616,  (1840). 

8  Stephan  Jahn,  Z.  f.  anorg.  Ch.  48,  260,  (1905). 

288 


THE    PRODUCTION    OF   OZONE  289 

Since  heat  is  absorbed  in  the  production  of  ozone,  thermo- 
dynamics requires  that  the  equilibrium  existing  in  a  mixture  of 
oxygen  and  ozone  be  displaced  in  the  direction  of  a  greater 
ozone  concentration  by  an  increase  in  the  temperature  of  the 
mixture.  In  order  to  prove  this  experimentally,  it  is  necessary 
to  heat  the  oxygen  to  a  temperature  high  enough  to  produce  a 
measurable  quantity  of  ozone,  and  then,  by  cooling  suddenly,  to 
prevent  the  decomposition  of  the  ozone  formed.  This  has  been 
done  by  blowing  air  or  oxygen  against  a  hot  pencil,  such  as  is 
used  in  a  Nernst  lamp,4  and  also  by  dipping  a  hot  Nernst 
pencil,  or  hot  platinum,  in  liquid  air.5 

The  free  energy  decrease  which  accompanies  the  decomposi- 
tion of  ozone  into  oxygen  has  been  determined  from  potential 
measurements.6  At  0°  C.  the  potential  of  the  cell  O3  |  electro- 
lyte H2  equals  1.90  volts,  and  that  of  the  cell  O2  |  electrolyte  H2 
equals  1.25  volts.  The  reactions  which  take  place  in  these  two 
cells,  with  the  corresponding  free  energy  changes,  are  therefore 
given  by  the  following  equations  : 

2  O3  +  2  H2  =  2  O2  +  2  H2O  +  4  F  x  1.90  joules, 
O2  +  2  H2  =  2  H2O  +  4  F  x  1.25  joules, 

where  F  is  the  electrochemical  equivalent.  The  difference 
between  these  two  equations  gives : 

2  O3  =  3  O2  +  4  F  x  0.65,  or  O3  =  f  O2  +  30,000  calories. 

From  this  result  the  following  equilibrium  concentrations  at 
high  temperatures  may  be  calculated : 

Temperature  on  absolute  scale      .     .  1000°      1400°       1800°     2200° 

Pres.  ozone  in  atmospheres,  in  equi- 
librium   with    oxygen    at    one 

atmosphere       0.000029     0.0032       0.038         0.18 

(0.007)     (0.03) 

The  above  results  are  only  approximate,  for  the  very  divergent 
values  inclosed  in  parentheses  are  within  the  experimental 
error. 

4  Fischer  and  Marx,  B.  B.  40,  443,  (1907). 

5  Fischer  and  Braemer,  B.  B.  39,  996,  (1906). 

6  Stephan  Jahn,  Z.  f.  anorg.  Ch.  60,  332,  (1908). 


290  APPLIED   ELECTROCHEMISTRY 

It  will  be  seen  from  these  results  that  ozone,  in  the  concen- 
trations ordinarily  prepared,  amounting  to  several  per  cent  by 
volume,  is  in  a  state  of  unstable  equilibrium,  and  it  conse- 
quently decomposes  slowly  on  standing.  This  reaction  is 
lii  molecular ; 7  that  is, 
•••'J'  dn  =  -kn*  dt, 

where  n  is  the  number  of  moles  per  cubic  centimeter,  k  is  a 
constant,  and  t  is  the  time.  The  velocity  of  this  reaction  is 
given  in  Table  39.  ft  is  the  number  of  grams  of  ozone  in  one 
liter  that  would  decompose  per  minute  if  its  initial  concentra- 
tion were  one  gram  per  liter. 

TABLE  39 


TEMPERATURE 

0 

16° 

0.0000492 

100° 

0.157 

126.9° 

1.77 

At  16°  one  per  cent  of  pure  ozone  would  decompose  in  1.7 
hours,  and  50  per  cent  in  167  hours.  These  values  apply  to 
ozone  in  contact  with  concentrated  sulphuric  acid,  over  which 
the  pressure  of  water  vapor  is  0.0021  millimeter  of  mercury. 
If  the  pressure  of  water  vapor  is  0.154  millimeter,  the  velocity 
of  decomposition  at  lOO^is  found  to  be  22  per  cent  greater. 

The  decomposition  of  ozone  takes  place  in  steps,  the  reaction 
whose  velocity  is  measured  being 

O  +  03  =  2  02.8 

Ozone  may  be  produced  by  the  action  of  ultra-violet  light, 
and  of  the  silent  discharge  of  electricity  on  oxygen ;  by  heat- 
ing and  suddenly  chilling  oxygen,  and  by  electrolysis.  While 
the  silent  electric  discharge  is  the  only  method  used  commer- 
cially for  the  manufacture  of  ozone,  it  will  be  interesting  to 

7  Warburg,  Ann.  d.  Phys.  9,  1286,  (1902),  and  13,  1080,  (1904). 

8  Jahn,  Z.  f.  anorg.  Ch.  48,  260,  (1005). 


THE    PRODUCTION    OF   OZONE  291 

compare  the  yield  per  kilowatt  hour  attained  by  the  silent  dis- 
charge with  some  of  the  other  methods.  By  blowing  air 
against  a  hot  Nernst  pencil,  the  yield  was  found  to  be  one 
gram  4  per  kilowatt  hour  ;  and  by  dipping  hot  bodies  in  liquid 
air,  about  3.5  grams.5  The  concentration  of  the  ozone  in  bot'^i 
cases  was  less  than  three  per  cent.  By  electrolyzing  solutions 
of  sulphuric  acid  of  specific  gravity  between  1.075  and  1.1 
with  a  water-cooled  platinum  anode,  as  high  as  17  per  cent  by 
weight  of  the  oxygen  given  off  at  the  anode  has  been  obtained 
in  the  form  of  ozone.9  Assuming  three  volts  sufficient  to 
electrolyze  the  solution,  the  yield  in  oxygen  per  kilowatt  hour 
would  be  10  grams,  and  if  17  per  cent  of  this  were  ozone,  the 
yield  would  be  only  1.7  grams  per  kilowatt  hour.  When  com- 
pared with  70  grams  per  kilowatt  hour,  the  yield  obtained  with 
the  silent  discharge,  these  methods  are  seen  to  be  inefficient 
from  an  economical  standpoint,  though  if  a  high  concentration 
is  desired,  this  can  be  best  obtained  by  electrolysis. 

There  are  two  distinct  forms  of  silent  discharge  of  electricity, 
which  differ  in  their  appearance,  in  the  amount  of  ozone  which 
they  produce,  and  in  the  current  which  is  required  to  produce 
them.10  If  a  point  one  centimeter  distant  from  a  plate  con- 
nected to  earth  is  charged  negatively  to  7000  volts  in  air,  a 
bluish  light  surrounding  the  point  can  be  seen  with  the  naked 
eye.  If  the  potential  is  raised,  a  reddish  broad  brush  appears, 
separated  from  the  bluish  light  by  a  dark  space,  while  the  oppo- 
site plate  remains  dark.  These  different  parts  of  the  discharge 
correspond  to  what  is  observed  in  a  vacuum  tube  in  which  the 
air  is  at  a  pressure  of  a  few  millimeters  of  mercury.  The 
bluish  light  corresponds  to  the  negative  glow,  the  dark  space 
to  the  Faraday  dark  space,  and  the  reddish  light  to  the  positive 
column  of  light. 

With  a  positively  charged  point  and  a  low  potential  differ- 
ence, a  reddish  envelope  of  light  is  first  observed,  from  which 
a  brush  is  developed  on  increasing  the  potential.  The  ability 

9  Fischer  and  Massenez,  Z.  f.  anorg.  Ch.  52,  202,  (1907). 
10  Askenasy,  Technische  Elektrochemie,  p.  240,  (1910);  and  Warburg,  Ber.  d, 
deutsch.  phys.  Ges.,  (1904),  209. 


292 


APPLIED   ELECTROCHEMISTRY 


to  form  this  brush  is  important  for  the  ozone  formation,  and  is 
lost  by  points  after  use.  In  place  of  it  a  spark  discharge  is 
produced  ;  but  the  brush  discharge  can  be 
produced  even  on  old  points  by  placing  a 
spark  gap  0.1  millimeter  long  before  the 
point. 

If  the  discharge  takes  place  between  paral- 
lel conducting  plates,  either  one  or  both  being 
covered  with  a  dielectric,  the  case  is  more 
complicated.11  This  type  of  ozonizer  was 
devised  by  W.  von  Siemens  and  is  usually 
called  by  his  name.12  Siemens's  original  ozon- 
izer consisted  of  concentric  tubes,  as  shown 
in  Figures  124  and  125.  Two  such  tubes, 
with  the  sides  a  and  d  covered  with  a  conduc- 
tor, such  as  tin  foil,  may  be  looked  upon  as  a 
series  of  condensers  connected  in  series,  with 
an  ohmic  resistance  in  parallel  with  one  of 
them.  In  this  case  there  would  be  three  con- 
densers :  ab,  be,  and  cd ;  while  if  the  inner 
tube  is  bare  metal  there  would  be  only  two  : 
be  and  ab.  When  the  space  be  is  filled  with  a 
perfect  insulator  or  with  a  perfect  conductor, 
the  current  has  its  small- 
est or  its  largest  value,  re- 
spectively. In  both  cases 
the  apparatus  is  a  perfect 
condenser  and  absorbs  no 
energy,  since  cos  <f>  =  0, 

FIG.    124.  —  Longi-  &J '       .  V.          ' 

tudinai  section  of  where  $  is   the   angle   of 

Siemens's  original    pnase     difference    between  FIG.  125  —  Transverse  sec- 

the  voltage  and  the  cur-  *»«"««M«.'.o«»,i»r 
rent.  For  an  average  conductivity  in  6<?,  such  as  a  gas  can 
have,  cos  <£  assumes  its  largest  value.  In  actual  practice  all 

11  Askenasy,  p.  242 ;    Warburg  and  Leithauser,  Ann.  d.  Phys.  28,   1  and 
17,  (1908). 

12  Fogg.  Ann.  102,  120,  (1857). 


THE    PRODUCTION   OF  OZONE  293 

possible  values  of  cos  <f>  between  0  and  1  may  occur.  With 
increasing  current  strength  cos  $  decreases,  probably  because 
the  resistance  of  the  gas  decreases  with  increasing  current.  If 
the  frequency  of  the  alternating  current  increases,  cos  <f>  in- 
creases and  approaches  1.  High  frequencies,  between  200  and 
500  per  second,  should  therefore  be  used.  Ozonizers  with  one 
tube  bare  metal  are  better  than  those  with  both  tubes  glass, 
for  cos  (j)  is  larger,  and  a  larger  current  passes,  for  a  given  vol- 
tage, than  in  a  glass  apparatus  of  the  same  dimensions. 

If  an  alternating  electromotive  force  is  applied  between  a 
point  electrode  and  a  plate  connected  to  earth,  the  positive 
brush  appears.  By  means  of  a  rotating  mirror  the  positive 
and  negative  light  can  be  seen  alternately  on  the  point,  and  its 
appearance  is  not  much  changed  when  the  plate  is  covered  with  an 
insulator.11  If  a  Siemens  apparatus  has  a  large  current  passing, 
a  uniform  luminosity  appears  in  the  space  between  the  elec- 
trodes, but  if  the  current  density  is  sufficiently  lowered,  brushes 
are  formed  at  single  points  on  the  electrodes.  From  the  ap- 
pearance of  these  discharges,  there  is  no  doubt  that  the  same 
process  takes  place  in  the  Siemens  apparatus  as  in  one  with 
point  and  plate  electrodes,  except  that  in  the  Siemens  ozonizer 
the  effects  on  positive  and  on  negative  points  are  superimposed, 
as  in  the  case  of  a  direct  current  between  two  metallic  points. 

The  production  of  ozone  by  the  silent  discharge  of  electricity 
may  be  considered  from  the  following  different  points  of  view  : 
(1)  the  maximum  concentration  that  can  be  obtained,  (2)  the 
maximum  number  of  grams  that  can  be  produced  per  coulomb 
of  electricity,  and  (3)  the  maximum  number  of  grams  per  unit 
of  power.  The  latter  consideration  is,  of  course,  of  the  most 
technical  importance.  As  stated  above,  ozonizers  with  point 
electrodes  give  different  results,  depending  on  whether  the 
points  are  positive  or  negative  to  the  plate.  The  Siemens  ozon- 
izer is  a  third  case  to  be  considered.  The  amount  of  ozone 
produced  per  coulomb  is  therefore  a  variable  quantity,  and  fol- 
lows no  known  law,  such  as  we  have  in  Faraday's  law  in  the 
case  of  electrolysis.  In  the  absence  of  such  a  law,  it  will  be 
necessary  to  show  what  the  yield  is  under  different  conditions 


294 


APPLIED   ELECTROCHEMISTRY 


and  how  this  is  affected  by  changing  the  conditions.  In  ordei 
to  give  a  systematic  survey  of  this  subject,  the  maximum  con- 
centration will  first  be  discussed  for  the  three  cases  enumerated 
above,  and  the  yields  per  unit  of  electricity 
and  per  unit  of  power,  including  the  factors 
that  affect  them,  will  then  be  taken  up  in  the 
following  order,  (1)  for  points  negative, 
(2)  for  points  positive,  and  (3)  for  Siemens 
ozonizers. 


0 


The  Maximum  Concentration 


The  silent  discharge  of  electricity  has  a 
deozonizing  effect  on  ozone,  as  well  as  an 
ozonizing  effect  on  oxygen.  The  ozonizing 
effect  of  the  discharge  is  proportional  to  the 
concentration  of  the  oxygen,  and  the  deozo- 
nizing effect  to  that  of  the  ozone.  In  other 
words,  this  reaction  follows  the  mass  action 
law.  If  the  discharge  passed  for  an  infinite 
time,  a  limiting  concentration  of  ozone  would 
be  reached,  at  which  the  amount  decomposed 
per  second  would  equal  the  amount  pro- 
duced. These  two  different  effects  have 
been  studied  separately  by  E.  Warburg.1 

The  experiments  were  carried  out  in  the 
apparatus  shown  in  Figure  126.  The  ozon- 
izer  0  was  connected  with  an  auxiliary  ves- 
sel H  by  a  capillary  tube  filled  with  sulphuric 
acid  to  a  proper  distance  above  B.  0  and 
H  each  had  a  volume  of  a  little  over  one 
cubic  centimeter.  The  point  electrode  el 
was  a  platinum  wire  0.05  millimeter  in  diam- 
eter; the  earth  electrode  02  was  a  platinum 
wire  0.5  millimeter  in  diameter  bent  in  the 
form  of  a  U  to  increase  the  surface.  After  filling  the  appara- 


FIG.  126.  —  Apparatus 
for  determining  the 
maximum  attaina- 
ble concentration  of 
ozone 


i  Ann.  d.  Phys.  9,  781,  (1900). 


THE    PRODUCTION   OF   OZONE 


295 


tus  with  oxygen  and  sealing  off  at  ^,  0,  and  5,  the  rate  at  which 
ozone  was  produced,  and  the  concentration,  could  be  observed 
by  the  change  in  the  height  of  the  sulphuric  acid  in  the  ma- 
nometer. Table  40  gives  the  results  obtained  with  el  connected 
to  the  negative  pole  of  an  electrostatic  machine  and  ez  through 
a  galvanometer  and  to  earth.  0  is  a  constant  proportional  to 
the  rate  of  formation  of  ozone  at  a  given  temperature,  and  a  is 
a  constant  proportional  to  its  decomposition. 


TABLE  40 


TEMPERATURE 

PEE  CENT  OZONE  BY 
VOLUME 

/3  =  A  CONSTANT  PRO- 
PORTIONAL TO  KATE 
OF  FORMATION 

o  =  A  CONSTANT  PRO- 
PORTIONAL TO  THE  RATE 
OF  DECOMPOSITION 

+  93 

1.23 

0.0177 

1.42 

50 

2.22 

0.0214 

0.939 

17 

3.53 

0.0225 

0.616 

0 

4.19 

0.0219 

0.503 

-71 

5.74 

0.0232 

0.380 

This  table  shows  that  the  maximum  concentration  decreases 
as  the  temperature  rises,  and  that  this  is  due  to  the  increasing 
decomposing  effect  of  the  discharge,  and  not 
to  a  smaller  ozonizing  effect.  This  is  evident 
from  the  values  of  a  and  /3.  The  spontaneous 
decomposition  of  the  ozone  was  negligible. 
The  ozonizer  was  then  replaced  by  the  one 
shown  in  Figure  127  with  a  volume  of  7.5 
cubic  centimeters.  The  point  electrode  e± 
consisted  of  a  platinum  wire  0.05  millimeter  FIG.  127.  — Ozonizer 
thick,  and  the  earth  electrode  e2  was  a  half 
cylindrical  platinum  plate.  In  this  ozonizer 
the  positive,  as  well  as  the  negative,  point  discharge  could  be 
obtained.  In  both  cases  faint,  luminous  points  were  visible  in 
the  dark  on  the  thin  wire,  while  the  earth  electrode  remained 
dark.  With  a  current  of  33  microamperes  the  results  in  Table 
41  were  obtained. 


296 


APPLIED   ELECTROCHEMISTRY 


TABLE  41 
Point  Electrode  Negative 


TEMP. 

MAXIMUM  CONCENTRA- 
TION  PEE  CENT  OZONE 
BY  VOL. 

/3=  CONST.  PROPORTIONAL  TO 
BATE  OP  FORMATION 

a  =  CONST.  PROPORTIONAL 
TO  KATE  OF  DECOM- 
POSITION 

48 

2.41 

0.00824 

0.332 

19 

3.38 

0.00807 

0.231 

0 

4.45 

0.00929 

0.198 

Point  Electrode  Positive 


48 

0.81 

0.00243 

0.297 

19 

1.06 

0.00258 

0.233 

0 

1.42 

0.00278 

0.198 

From  these  results  it  is  evident  (1)  that  the  maximum 
concentration  with  the  point  negative  is  about  three  times  as 
great  as  with  the  point  positive  ;  (2)  that  this  is  due  to  the 
greater  ozonizing  effect  of  the  discharge  when  the  point  is 
negative,  since  the  deozonizing  effect  is  approximately  the  same 
in  both  cases  ;  and  (3)  the  temperature  effect  is  the  same  for 
the  positive  as  for  the  negative  point  discharge. 

For  the  Siemens  type  of  apparatus  the  limiting  concentration 
of  ozone  produced  from  96  per  cent  oxygen  diminishes  slightly 
with  increasing  current,  as  shown  by  the  following  table : 2 

TABLE  42 


TEMPBRATTTBE 

AMPEKKS  x  108 

OZONE 

GRAMS  PER  CUBIC 
METER 

PER  CENT  BY 
VOLUME 

19 
19 

1.21 
3.00 

168 
165 

8.02 
7.90 

Apparatus  changed 


24 
24 

1.33 
2.16 

114 
110 

5.46 
5.27 

2  Warburg  and  Leithauser,  Ann.  der  Phys.  28,  31,  (1909). 


THE    PRODUCTION   OF  OZONE 


297 


FIG.  128.—  Experimental  ozonizer 


Fig.  129.  — Experimental  ozonizer 


298 


APPLIED    ELECTROCHEMISTRY 


The  limiting  concentration  is  evidently  a  quantity  that 
varies  with  the  apparatus  used.  The  highest  value  obtained 
is  211  grams  per  cubic  meter,  or  10.1  per  cent  by  volume.3 


Yield  per  Coulomb  for  Negative  Point  Electrode 

In  order  to  produce  the  maximum  amount  of  ozone  per 
coulomb,  the  deozonizing  effect  of  the  electric  discharge  must 

be  excluded.  This  may  be  ac- 
complished by  passing  the  oxy- 
gen through  the  ozonizer  so 
rapidly  that  the  concentration 
of  the  ozone  produced  remains 
very  low  compared  with  the 
maximum  concentration  attain- 
able. In  a  number  of  the  ex- 
periments referred  to  below, 
the  concentration  of  ozone  did 
not  exceed  one  per  cent  of  the 
maximum.  A  number  of  dif- 
ferent forms  of  apparatus  with 
a  point  electrode  were  used  by 
Warburg  in  determining  these 
yields.  In  the  apparatus  shown 
in  Figure  128,  E,  the  earth 
electrode,  is  a  platinum  plate ; 
in  Figure  129  E  is  a  platinum 
cylinder  ;  and  in  Figure  130, 
consisting  of  a  liter  bottle,  E  is 
concentrated  sulphuric  acid. 
Figure  131  shows  an  ozonizer 
with  a  number  of  point  elec- 
trodes. 

FIG.  130.— Experimental  ozoiiizer  „ 

With  the  point  negative,  for 
a  given  current  strength  the  yield  per  coulomb  is  independent 


•  Warburg  and  Leithauser,  Ann.  der  Phys.  28,  25,  (1909). 


THE    PRODUCTION    OF   OZONE 


299 


of  the  voltage,  as  shown  by  the  results  of  Table  43,1  obtained 
with  oxygen  93  per  cent  pure  by  volume.  In  the  following 
tables  the  current  given  is  for  one  point  only,  in  case  the  appa- 
ratus contained  more  than  one  point. 


TABLE  43 


AMPERES  x  10« 

VOLTS 

GRAMS  OZONE  PER  COULOMB 

57 

4200 

0.0375 

57.5 

9880 

0.0386 

57.2 

11,700 

0.0387 

FIG.  131.  —Experimental  ozonizer 

The  yield  is  also  independent  of  the  form  of  the  anode,  and 
decreases  slowly  with  increasing  current,  as  is  shown  by  the 
following  results  obtained  with  different  forms  of  anode  : l 


Warburg,  Ann.  der  Phys.  13,  472,  (1904). 


300 


APPLIED   ELECTROCHEMISTRY 
TABLE  44 


APPARATUS  IN  FIG.  128 

APPARATUS  IN  FIG.  129 

Amperes  x  106 

Grams  Ozone  per 
Coulomb 

Amperes  x  106 

Grams  Ozone  per 
Coulomb 

17.4 

0.0484 

29.1 

0.0431 

25.1 

0.0459 

57.5 

0.0386 

57.2 

0.0375 

94.2 

0.0370 

These  results  are  for  the  case  where  negative  light  appears 
only  on  the  point.  If  it  appears  at  other  parts  of  the  electrode, 
the  yield  may  increase  with  the  current.  The  yield  depends 
further  on  whether  the  points  have  been  previously  used,  being 
greater  for  previously  used  points  :  2 

TABLE  45 
Oxygen,  96  per  cent  pure,  by  volume 


TIME  DURING  WHICH 
OZONIZER  WAS  USED 
BETWEEN  EXPERIMENTS 

VOLTS 

AMPERES  x  106 

GRAMS  OZONE  PER 
COULOMB 

_^__ 

6080 

14.6 

0.0408 

125  min. 

6960 

21.9 

0.0452 

165  min. 

6420 

17,6 

0.0803 

75  min. 

6300 

17.5 

0.0873 

30  min. 

8800 

17.5 

0.0908 

This  increase  in  the  yield  is  accompanied  by  a  change  in  the 
character  of  the  light  on  the  electrode.  When  the  final  state 
of  the  electrode  has  been  reached  the  yield  decreases  for  increas- 
ing current  to  a  certain  point,  as  shown  by  the  results  in  Table 
46  of  experiments  with  98.5  per  cent  oxygen  :3 


2  Warburg,  Ann.  d.  Phys.  17,  6,  (1905), 
*  Warburg,  Ann.  d.  Phys.  17,  6,  (1905). 


THE    PRODUCTION    OF   OZONE 
TABLE  46 


301 


GRAMS  OZONE  PER 

GRAMS  OZONE  PER 

VOLTS 

AMPEBES  x  106 

COULOMB 

KILO  WATT-HOUR 

7230 

8.83 

0.0950 

47.3 

8800 

17.50 

0.0908 

37.1 

12,500 

52.30 

0.0485 

14.0 

If  the  current  is  increased  to  a  still  higher  value,  the  yield 
reaches  a  minimum  and  then  increases  with  the  current.  This 
is  shown  by  the  results  in  Table  47,  obtained  with  new  points 
and  with  oxygen  96  per  cent  pure  by  volume : 4 

TABLE  47 


VOLTS 

AMPERES  x  106 

GRAMS  OZONE  PER 
COULOMB 

6080 

14.6 

0.0423 



21.9 

0.0340 

9610 

52.4 

0.0307 

12,510 

130.7 

0.0422 

7000 

21.9 

0.0375 

In  this  case  also  a  marked  change  in  the  appearance  of  the 
light  accompanies  the  increase  in  the  yield  after  passing  the 
minimum.  After  a  certain  amount  of  practice,  it  is  even  pos- 
sible to  predict  from  the  appearance  of  the  light  what  the  yield 
will  be.6 

In  changing  the  temperature  and  pressure  of  the  gas,  not  only 
the  substance  which  is  to  be  acted  upon  is  altered,  but  also 
the  agent  which  brings  about  the  reaction  ;  for  the  light  changes 
its  character  when  the  physical  state  of  the  gas  through  which 
the  current  is  passed  is  altered.  This  fact  complicates  the 
study  of  this  subject.  The  results  in  Table  48  with  oxygen 
98.5  per  cent  pure  by  volume  show  how  the  yield  increases 
with  the  pressure  : 6 

4  Ann.  d.  Phys.  17,  10,  (1905).  6  Ann.  d.  Phys.  17,  7,  (1905). 

e  Ann.  d.  Phys.  17,  12,  (1905). 


302 


APPLIED   ELECTROCHEMISTRY 
TABLE  48 


PRESSURE  IN  MM. 
OF  MERCURY 

VOLTS 

GRAMS  OZONE  PER 
COULOMB 

REMARKS 

460 

3810 

0.0365 

Points    previously    sub- 

784 

5220 

0.0522 

jected  to  long  use.  Current 

1210 

6900 

0.0903 

=  37.4  x  10~6  ampere 

465 

5520 

0.0355 

Fresh    points.     Current 

780 

7410 

0.0477 

=  17.5  x  10~6  ampere 

1208 

9700 

0.0597 

Between  780  and  460  millimeters  pressure,  the  yield  Ap  for  any 
pressure  p  is  given  by  the  equation 7 

Ap  =  A7QO  [1  -  (760  -p)  0.00089]. 

The  temperature  of  the  gas  in  all  of  these  experiments  lay 
between  17°  and  23°.  Table  49  shows  the  effect  on  the  yield 
of  changing  the  temperature  : 

TABLE  49 
Oxygen  98.5  per  cent  pure  by  Volume.    Current  37.4  X  10~6  Ampere 


PRESSURE  IN 
MM.  OP  MERCURY 

TEMPERATURE 

VOLTS 

GRAMS  OZONE  PER 
COULOMB 

785 

16.5 

7530 

0.0418 

782 

79.5 

6560 

0.0376 

789 

14.8 

7500 

0.0430 

789 

80.1 

6440 

0.0395 

788 

14.2 

7470 

0.0430 

780 

79.7 

6320 

0.0387 

786 

15.4 

7350 

0.0429 

786 

79.8 

6320 

0.0394 

This  decrease  in  the  yield  is  largely  due  to  the  decrease  in  the 
density  of  the  oxygen  when  the  temperature  is  raised.  If  the 
pressure  is  increased  enough  to  keep  the  density  constant, 
the  yield  is  very  little  affected.  This  is  shown  in  Table  50, 
obtained  with  points  not  previously  used  : 
7  Ann.  d.  Phys.  28,  21,  (1909). 


THE    PRODUCTION   OF   OZONE 
TABLE  50 


303 


PRESSURE  IN  MM. 
OP  MERCURY 

TEMPERATURE 

VOLTS 

AMPERES  x  106 

GRAMS  OZONE  PER 
COULOMB 

783    s 

12.4: 

6440 

17.5 

0.0403 

951 

80.0 

5970 

17.5 

0.0413 

775 

11.8 

6350 

17.5 

0.0458 

963 

80.0 

6180 

17.5 

0.0480 

782 

10.4 

10,190 

52.4 

0.0389 

979 

80.3 

8860 

52.4 

0.0370 

792 

15.0 

9470 

52.4 

0.0394 

980 

80.0 

8920 

52.4 

0.0388 

It  is  therefore  evident  that  if  the  density  is  constant,  the  yield 
is  changed  only  a  few  per  cent  between  10  and  80  degrees. 

The  relation  between  the  yield  per  coulomb  and  the  concen- 
tration of  the  ozone  produced  from  98  per  cent  oxygen  is  linear.8 
If  the  concentration  is  allowed  to  reach  12.9  grams  per  cubic 
meter,  the  yield  falls  to  75  per  cent  of  its  value  for  a  concentra- 
tion of  1.3  to  1.6  grams  per  cubic  meter.  The  formula 

^  =  0.166-  0.00215 c 

gives  the  yield  per  coulomb  for  different  values  of  the  concen- 
tration c  between  1.6  and  12.9  grams  per  cubic  meter,  and  for 
a  current  of  0.0175  x  10~3  ampere.  The  yield  per  kilowatt 
hour  is  given  by  the  equation  : 

B  =  71.0  -  1.58  c  +  0.00090  c2. 

These  results  were  obtained  with  spheres,  in  place  of  points,  1.5 
to  2  millimeters  in  diameter,  melted  on  a  wire  1  millimeter  in 
diameter.  The  yield  for  this  kind  of  electrode  is  much  higher 
than  for  points,  and  when  used  as  the  positive  pole,  spheres  do 
not  show  the  aging  effect  that  is  observed  with  points. 

The  presence  of  water  vapor  in  oxygen  reduces  the  yield 
nearly  proportionally  to  the  pressure  of  the  water  vapor.9 
The  reduction  in  the  yield  for  seven  millimeters  pressure  is 

s  Warburg  and  Leithauser,  Ann.  d.  Phys.  20,  734,  (1906). 
9  Ann.  d.  Phys.  20,  751,  (1906). 


304 


APPLIED   ELECTROCHEMISTRY 


about  94  per  cent  of  its  value  for  dry  oxygen.  There  is  also 
a  great  tendency  for  the  formation  of  sparks  when  the  gas  is 
moist. 

When  oxygen  is  mixed  with  only  7  per  cent  of  nitrogen,  the 
silent  discharge  produces  no  oxide  of  nitrogen,10  but  when  air 
is  used  oxides  of  nitrogen  are  produced.  The  spark  discharge 
produces  only  oxides,  and  these  prevent  the  formation  of 
ozone.11  For  air,  the  yield  per  coulomb  is  independent  of  the 
voltage  for  a  constant  current,  as  in  the  case  of  oxygen,  but  it 
is  much  smaller  than  for  oxygen.  This  is  shown  in  Table  51. M 

TABLE  51 
Air.    Temperature  20°.     Six  Points.    Current  for  One  Point  =  21.9  X  10-6  ampere 


VOLTS 

DISTANCE    BETWEEN 
POINT  AND  PLATE  IN 
MILLIMETERS 

GRAMS   OZONE  PER 
COULOMB 

8240 

12.8 

0.0112 

8300 

12.8 

0.0110 

3930 

3.4 

0.0110 

7950 

13.5 

0.0110 

For  air,  the  yield  first  decreases  with  increasing  current  and 
reaches  a  minimum,  after  which  it  increases  more  rapidly  than 
for  oxygen,  as  shown  in  Table  52. 

TABLE  52 


AMPERES  x  106 

VOLTS 

DISTANCE    BETWEEN 
POINT  AND  PLATE  IN 
MILLIMETERS 

GRAMS  OZONE  PER 
COULOMB 

21.9 

8300 

12.8 

0.01100 

54.5 





0.00935 

55.2 

7830 

7.5 

0.00766 

163.0 

12,200 

7.5 

0.01880 

219.0 

12,940 

7.5 

0.02500 

10  Warburg,  Ann.  d.  Phys.  13,  470,  (1904). 

11  Warburg  and  Leithauser,  Ann.  d.  Phys.  20,  743,  (1906). 

12  Warburg,  Ann.  d.  Phys.  17,  25,  (1905). 


THE    PRODUCTION   OF   OZONE  305 

The  change  that  takes  place  in  the  luminosity  when  the  yield 
begins  to  increase  is  similar  to  that  in  the  case  of  oxygen. 

The  effect  of  the  concentration  of  the  ozone  produced  on  the 
yield  in  air  is  approximately  the  same  as  in  oxygen.13  A,  the 
yield  in  grams  per  coulomb,  and  B,  the  yield  in  grams  per  kilo- 
watt hour,  are  given  by  the  following  equations,  for  values  of 
the  concentration  c  between  2.19  and  9.62  grams  per  cubic 
meter  : 

A  =  0.0780  -  0.00220  c, 

B  =  42.6  -  1.60  c  +  0.0036  c  2. 

The  effect  of  moisture  is  greater  for  air  than  for  oxygen,  7 
millimeters  pressure  of  water  vapor  reducing  the  yield  to  69. 7 
per  cent  of  its  value  for  dry  air.14 

The  effect  of  temperature  on  the  yield  for  negative  points 
in  air  has  not  been  determined. 


Yield  per  Coulomb  for  Positive  Point  Electrode 

The  effect  of  increasing  the  current  on  a  positive  point 
electrode  is  quite  different  from  the  effect  on  a  negative  point. 
With  positive  points  the  yield  is  smallest  for  small  currents, 
but  increases  as  soon  as  the  positive  brush  appears,  and,  with 
points  not  previously  used,  it  finally  reaches  values  exceeding 
the  highest  ones  obtainable  with  negative  points.  This  is 
shown  in  Table  53. l  The  yield  is  very  much  affected  by  the 
character  of  the  positive  brush,  which  depends  on  a  number  of 
circumstances  difficult  to  control. 

The  effects  of  temperature  and  pressure  on  the  yield  with 
positive  points  in  oxygen  have  not  been  investigated. 

The  relation  between  the  yield  in  grams  per  coulomb,  A,  and 
the  concentration  of  ozone,  <?,  produced,  is  given  by  the  equa- 
tion: 

-4  =  0.166-  0.00853  c, 

13  Warburg  and  Leithauser,  Ann.  d.  Phys.  20,  734,  (1906). 
"  Ann.  d.  Phys.  20,  734,  (1906). 
i  Warburg,  Ann.  d.  Phys.  17,  19,  (1905). 
x 


306 


APPLIED   ELECTROCHEMISTRY 


which  holds  for  values  of  c  between  1.18  and  8.49  grams  per 
cubic  meter.2  The  corresponding  equation  for  grams  per 
kilowatt  hour  is 

£  =67.0- 3.44  c. 

These  results  are  for  spheres  in  place  of  points,  and  for  a 
current  on  one  sphere  of  0.033  x  10~3  ampere. 


TABLE  53 
93  per  cent  Oxygen  by  Volume 


DISTANCE 

GRAMS  OZOXE 

WIRE  OF  +  POLE 
IN  MILLIMETERS 

BETWEEN 

POLES  IN 
MILLIMETERS 

CENTI- 
GRADE 

YOLTS 

AMPERES 
xlO« 

Per 

Coulomb 

Per 
Kilowatt 
Hour 

0.1 

13.5 

16 

12,900 

77.2 

0.0372 

10.4 

0.5 

3.6 

17 

5710 

22.9 

0.0499 

31.4 

0.5 

13.5 

16 

12,900 

87.4 

0.0795 

22.2 

1.0 

4.0 

18 

6900 

42.5 

0.0871 

45.4 

1.0  copper 

4.0 

18 

5590 

29.4 

0.0760 

48.9 

1.0 

4.0 

18 

5970 

43.9 

0.0856 

51.5 

98.5  per  cent  Oxygen 


1 

2 

4.4 

5 

20 
19 

7830 
7710 

47.9 
62.4 

0.0947 
0.0680 

43.8 
31.8 

The  reduction  in  the  yield  by  water  vapor  is  much  greater 
for  positive  points  in  oxygen  than  for  negative.  When  the 
vapor  pressure  of  the  water  is  seven  millimeters,  the  yield  is 
only  64  per  cent  of  its  value  for  dry  oxygen.3 

Positive  points  in  air  act  similarly  to  positive  points  in 
oxygen,  except  that  the  positive  brush  is  more  capricious  in 
air.4  The  yield  is  much  smaller  than  for  negative  points  as 
long  as  no  positive  brush  appears,  and  while  the  positive  glow 
covers  the  point  in  a  thin  layer;  but  with  the  appearance  of 

a  Warburg  and  Leithauser,  Ann.  d.  Phys.  20,  739,  (1906). 

3  Ann.  d.  Phys.  20,  753,  (1906). 

*  Warburg,  Ann.  d.  Phys.  17,  26,  (1905). 


THE    PRODUCTION   OF   OZONE 


307 


the  positive  brush  the  yield  increases  and  reaches  values  much 
higher  than  any  obtained  with  negative  points  in  air.  This 
will  be  seen  from  the  results  of  Table  54. 

TABLE  54 
Atmospheric  Air.    Positive  Points  of  wire  0.25  mm.  in  Diameter 


GRAMS  OZONE 

DISTANCE  BETWEEN 
POINT  AND  PLATE 

VOLTS 

AMPERES  x  106 

Per  Coulomb 

Per  Kilowatt  Hour 

13.5 

7950 

14.6 

0.00294 



13.5 

8060 

14.5 

0.00288 



7.5 

8060 

32.7 

0.00307 



3.5 

5340 

36.4 

0.0377 

25.4"!  Voltage  near 

3.5 

5340 

36.4 

0.0387 

26.1  [•      sparking 

9.8 

10,800 

100.7 

0.0505 

16.8  J      point 

The  yield  in  grams  per  coulomb,  A,  and  in  grams  per 
kilowatt  hour,  J9,  in  air  are  given  by  the  equations: 

.4  =  0.114-  0.008670, 
B  =  60  -  6  e 

for  values  of  c  between  0.58  and  3.94  grams  per  cubic 
meter. 

The  effect  of  water  vapor  on  the  yield  with  positive  points  in 
air  is  the  greatest  of  any  so  far  considered.  In  this  case,  for  a 
pressure  of  water  vapor  of  7  millimeters,  the  yield  falls  to 
49.1  per  cent  of  its  value  for  dry  air. 

It  is  evident,  from  the  fact  that  positive  points  near  the 
sparking  potential  give  a  better  yield  than  negative  points, 
both  for  oxygen  and  for  air,  that  if  an  alternating  current  is 
used  the  yield  will  not  be  as  good  as  with  a  direct  current  with 
positive  points,  for  with  an  alternating  current  the  points  will 
be  negative  half  of  the  time.  This  has  been  tested  by  direct 
comparison  for  oxygen  and  air.  The  results  are  given  in 
Table  55.6 


6  Warburg,  Ann.  d.  Phys.  17.  29,  (1905), 


308 


APPLIED   ELECTROCHEMISTRY 


TABLE  55 
98.5  per  cent  Oxygen.    Temperature  19 


GRAMS  OZONE 

DISTANCE  OF 

POINT  FROM 

CURRENT 

VOLTS 

AMPERES  x  10« 

PLATE  IN  MM. 

Per  Coulomb 

Per  Kilo- 

watt Hour 

6.8 

Alternating 

6780 

53.0 

0.0258 

13.7 

6.8 

Direct 

8860 

70.8 

0.0612 

24.9 

4.4 

Alternating 

5340 

37.0 

0.0128 

8.6 

4.4 

Direct 

7830 

47.9 

0.0947 

43.5 

Atmospheric  Air 


5 

Alternating 

5220 

42.0 

0.0190 

13.0 

5 

Direct 

6720 

52.6 

0.0523 

28.2 

5 

Alternating 

5590 

62.1 

0.0142 

9.1 

5 

Direct 

7120 

54.2 

0.0443 

22.4 

The  Yield  per  Kilowatt  Hour  for  Positive  and  for 
Negative  Points 

It  is  evident  from  what  has  preceded  that  the  yield  per  unit 
of  energy  depends  on  a  large  number  of  factors.  For  negative 
points,  it  is  best  to  use  the  smallest  possible  current  and  a  short 
distance  between  the  points  and  the  plate,  and  the  points  should 
not  be  fresh.  For  positive  points,  heavy,  new  wires  one  milli- 
meter thick  are  best,  and  the  potential  should  be  as  high  as 
possible  without  producing  sparks.  The  distance  between 
point  and  plate  should  not  be  too  great,  for  though  the  yield 
per  coulomb  increases,  the  yield  per  kilowatt  hour  decreases,  as 
seen  in  Table  54. 

Much  better  yields  both  for  positive  and  for  negative  points 
are  obtained  by  substituting  small  spheres  1.5  to  2  millimeters 
in  diameter  for  the  points,  as  is  seen  in  the  results  on  the  effect 
of  concentration  on  the  yield  of  ozone.  It  can  be  calculated 
from  the  equations  given  above,  that  for  air,  concentrations  up 
to  4  grams  per  cubic  meter  are  produced  most  economically 


THE    PRODUCTION   OF   OZONE  309 

when  the  points  are  positive  and  the  current  high,  while  con- 
centrations between  4  and  9  grams  per  cubic  meter  are  most 
economically  produced  with  negative  points  and  low  currents.1 
About  30  grains  per  kilowatt  hour  can  be  obtained  in  the  latter 
case  for  a  concentration  of  8  to  9  grams  per  cubic  meter. 

Theory  of  Ozone  Formation  by  the  Silent  Discharge 

That  the  formation  of  ozone  is  not  electrolytic  in  its  nature  1 
can  be  shown  from  the  yields  given  above,  which  vary  between 
0.003  and  0.1  gram  per  coulomb.  Since  one  equivalent  of 
hydrogen  reduces  24  grams  of  ozone,  24  may  be  taken  as  the 
latter's  equivalent  weight.  The  number  of  coulombs  required 
to  produce  24  grams  of  ozone  therefore  lies  between  8000  and 
240,  numbers  not  at  all  comparable  with  the  electrochemical 
equivalent,  96,540  coulombs.  On  the  other  hand,  the  energy 
required  is  considerably  greater  than  the  heat  of  the  reaction. 
On  the  basis  of  the  highest  yield  of  70  grams  per  kilowatt  hour 
(see  the  equation  for  yield  with  negative  points  in  oxygen),  the 
energy  required  for  one  mole  of  ozone  is  589,000  calories,  20 
times  as  much  as  the  heat  of  the  reaction.  Warburg's  theory 
is  that  ozone  is  formed  by  those  electrons  that  have  a  velocity  as 
high  as  that  required  for  the  production  of  luminosity.  Ozone 
may  be  formed  directly  by  the  impact  of  such  electrons  with 
oxygen  molecules  or  by  the  intermediate  production  of  short 
ether  waves.2 

The  Siemens   Ozonizer  l 

The  effect  of  pressure  is  the  same  in  a  Siemens  ozonizer  as 
for  a  point  and  plate,  both  being  represented  by  the  formula 
given  above  : 

A  =  Aeo[l  -(760-^)0.00089]. 

1  Warburg  and  Leithauser,  Ann.  d.  Phys.  20,  742,  (1906). 

1  Warburg,  Ann.  d.  Phys.  13,  474,  (1904). 

2  Warburg,  Ann.  d.  Phys.  17,  7,  (1905). 

1  Warburg  and  Leithauser,  Ann.  d.  Phys.  28,  17,  (1909).  The  following  dis- 
cussion is  taken  from  this  article,  except  where  other  references  are  given. 


310 


APPLIED    ELECTROCHEMISTRY 


In  air  the  pressure  of  oxygen  is  160  millimeters,  and  in  96  per 
cent  oxygen,  730  millimeters.  Substituting  these  values  in  the 
above  equation, 


This  relation  is  verified  by  the  following  results,  in  which  the 
gas  was  passed  through  the  ozonizer  at  such  a  rate  that  the 
concentration  remained  low.  The  effective  current  was  meas- 

ured. 

TABLE  56 


GRAMS  OZONE  PER  COULOMB 

CURRENT  PER 

-^160 

SQUARE  METER 

In  Oxygen 

In  Air 

0.146 

0.0634 

0.0194 

0.31] 

50    alternations    per 

0.193 

0.151 

0.0662 

0.44  I 

second.      Apparatus  :    2 

0.133 

0.238 

0.115 

0.49  j 

concentric  glass  tubes 

0.159 
0.182 

0.216 
0.204 

0.106 
0.106 

0.48] 
0.52  \ 

Central  tube   is  bare 

metal 

0.182 

0.288 

0.146 

0.51  J 

The  quantity  of  ozone  produced  per  coulomb  for  a  given 
apparatus  increases  with  the  potential  as  in  the  case  of  positive 
points,  and  the  effect  of  water  vapor  is  to  lower  the  yield.2 

A  factor  not  considered  in  Warburg's  work,  but  one  which 
has  a  great  effect  on  the  yield,  is  the  transparency  of  the  glass 
of  the  ozonizer  for  ultra-violet  light.3  An  ozonizer  of  quartz, 
for  example,  which  is  transparent  to  ultra-violet  rays,  gives 
only  half  as  much  ozone,  other  conditions  being  equal,  as  a 
glass  ozonizer  of  the  same  dimensions. 

The  relation  between  the  yield  and  the  concentration  of  the 
ozone  leaving  the  ozonizer  is  similar  to  that  for  points,  and  is 
given  in  Table  57. 

The  formation  of  ozone  is  proportional  to  the  mean  current, 


—       idt,  and  not  to  the  effective  current, 


1   C 

-«J 


tne  value 


2  A.  W.  Gray,  Phys.  Rev.  19,  362,  (1904). 
»  F.  Russ,  Z.  f.  Elektroch.  12,  409,  (1906). 


THE    PRODUCTION    OF   OZONE 


311 


given  by  measuring  instruments  ;  consequently,  if  the  effective 
current  is  measured,  the  yield  will  also  depend  on  the  wave 

form  of  the  current. 

TABLE  57 

Oxygen  96  per  cent  pure.    Maximum  Concentration  of  Ozone  equals  168  Grams 
per  cubic  meter 


CONC.  OZONE  IN  GKAMS 
PER  CUBIC  METER 

GRAMS  OZONE  PER 
COULOMB 

CONC.  OZONE  IN  GRAMS 
PEE  CUBIC  METER 

GRAMS  OZONE  PER 
COULOMB 

16.1 

0.121 

53.1 

0.104 

23.2 

0.120 

62.4 

0.102 

29.9 

0.116 

68.4 

0.100 

31.2 

0.115 

80.6 

0.095 

41.1 

0.111 

The  effect  of  temperature  is  similar  to  that  in  the  apparatus 
with  point  and  plate  electrodes :  the  yield  for  zero  concentra- 
tion changes  very  little,  while  the  deozonizing  effect  of  the 
current  on  the  ozone  already  formed  increases  with  the  temper- 
ature. 

The  yield  per  kilowatt  hour  is  greater  where  one  electrode  is 
not  covered  with  an  insulator,  because  of  the  greater  current 
for  a  given  voltage  and  the  greater  value  of  cos  <f>.  The  thick- 
ness of  the  dielectric  has  no  effect.4  The  following  table  gives 
the  yield  obtained  by  Warburg  and  Leithauser  in  grams  ozone 
per  kilowatt  hour.5 

TABLE  58 

Air 


GRAMS  PER  KILOWATT- 

DISTANCE  BETWEEN 
PLATES  IN  MM. 

FREQUENCY 

HOUR  FOR 

AMPERES  PER  SQUARE 
METER 

Cone.  =4 

Cone.  =  10 

grms.  per 

grins,  per 

ma. 

m3. 

2.26 

50 

78.4 

72.2 

0.182 

2.26 

100 

81.4 

75.7 

0.308 

2.26 

500 

66.0 

57.1 

1.580 

4.66 

50 

62.4 

53.3 

0.169 

4.66 

100 

63.0 

54.0 

0.280 

4.66 

500 

58.0 

33.0 

1.190 

4  See  also  Ewell,  Phys.  Rev.  22,  243,  (1906). 
6  Ann.  d.  Phys.  28,  36,  (1909). 


312 


APPLIED    ELECTROCHEMISTRY 


It  will  be  noticed  that  the  yield  for  a  Siemens  ozonizer  is 
considerably  higher  than  for  those  having  a  point  and  a  plate 
electrode,  for  which  the  highest  value  was  36  grams  per  kilo- 
watt at  a  concentration  of  4  grams  per  cubic  meter. 

2.    THE  TECHNICAL  PRODUCTION  OF  OZONE 

Ozone  is  produced  commercially  for  the  purification  of  water, 
for  bleaching,  and  for  use  as  an  oxidizing  agent  in  organic 

chemistry.1  In  water  pu- 
rification, the  action  of 
ozone  is  to  oxidize  the 
organic  matter  and  to 
destroy  germs. 

Siemens  and  Halske 
make  the  ozone  apparatus 
shown  in  Figure  132. 2 
The  discharge  chamber  is 
between  two  concentric 
metal  cylinders,  between 


la 


'Ozone 


FIG.  132.  —  The  Siemens  and  Halske  ozonizer 

which  8000  volts  alternating  are  applied.     The  cylinders  are 


Cooling  Water 


T 


FIG.  133.  — The  Tindal  ozonizer 


immersed  in  water  for  cooling,  and  the  outer  one  is  connected 
to  earth.     One  of  the  surfaces  from  which  the  discharge  takes 


1  J.  W.  Swan,  Z.  f.  Elektroch.  7,  950,  (1901). 

2  Z.  f.  Elektroch.  10,  13,  (1904);  Electrochem.  Ind.  2,  67,  (1904). 


THE    PRODUCTION   OF   OZONE 


313 


TPef,fugrat03r 


place  is  covered  with  a  glass  dielectric.  Air  enters  at  the  top, 
is  partly  changed  to  ozone  in  passing  between  the  walls  of  the 
concentric  cylinders,  and  leaves  the  apparatus  from  below. 
The  concentration  of  the  ozone  is  about  2  grams  per  cubic 
meter,  which  is  high  enough  for  all  ordinary  purposes.  The 
yield  varies  between  18  and  37  grams  per  kilowatt  hour.3 

The  Tindal  ozonizer  is 
shown  in  Figure  133. 
It  is  in  the  form  of  a 
box,  the  inner  walls  of 
which  are  water-cooled 
electrodes  and  are  con- 
nected to  earth.  The 
other  electrodes  are  metal 
plates  inside  the  box  and 
insulated  from  it.  Be- 
tween 40,000  and  50,000 
volts  are  applied  to  the 
electrodes. 

The        Abraham-Mar- 

rnier2  apparatus  is  shown  in  Figure  134.  It  consists  of  a  num- 
ber of  cylindrical,  parallel,  hollow  electrodes  of  about  a  square 
meter  area,  covered  with  glass  and  mounted  in  a  box.  Water  cir- 
culates through 
the  electrodes 
for  cooling,  be- 
tween which 
about  40,000 
volts  are  ap- 
plied. 

The       Otto 
apparatus 4       is 


FIG.  134. — The  Abraham-Marmier  ozonizer 


The  Otto  ozonizer 

FIG.  135.  —  Longitudinal-vertical  FIG.  136.  —  Transverse 

section  vertical  section  ,  .        ,,,. 

shown    in    r  ig- 

ures  135  and  136.     It  consists  of  a  chamber,  K,  the  metal  wall, 
EV  of  which  forms  one  electrode.     The  sheet  steel  rings,  $, 

»  Askenasy,  Elektrochemie,  1,  246,  (1910). 
*  Z.  f.  Elektroch.  7,  790,  (1901). 


314 


APPLIED   ELECTROCHEMISTRY 


sharpened  at  M,  and  mounted  on  an  axle  on  which  they  rotate, 
are  the  other  electrode,  E%.  There  is  no  solid  dielectric.  Air 
passes  in  the  box  at  B  arid  comes  .out  at  A.  While  in  the  box 
it  is  ozonized  and  thoroughly  mixed  by  the  rotating  electrode. 
If  an  arc  were  to  form  between  the  electrodes,  it  would  be  ex- 
tinguished as  the  grooves  RR  in  the 
rotating  electrode  pass  the  insulat- 
ing base  of  the  box,  aa.  About  25,000 
volts  are  applied  to  the  electrodes, 
the  distance  between  which  may  be 
from  10  to  100  millimeters. 

Small  ozonizers  are  now  made  for 
sterilizing  water  where  it  is  drawn 
for  use,  as  shown  in  Figure  137. 5 
The  transformer  and  ozonizer  are  in 
a  metal  case,  0.  P  and  S  are  respec- 
tively the  primary  and  the  secondary 
of  the  transformer.  The  primary  is 
supplied  with  100  to  250  volts,  which 
is  transformed  to  15,000  volts  in  the 
secondary.  The  ozonizer  consists  of 
six  or  more  glass  plates,  6r,  supported 
on  a  grooved  bracket  at  the  bottom, 
and  by  grooved  slips  at  the  sides  and 
top.  Three  pairs  of  plates,  each  plate 
covered  on  one  side  with  tin  foil,  are 
shown  in  the  sketch.  The  discharge 
takes  place  between  two  opposite 
FIG.  137.  —  Small  ozonizer  con-  sheets  of  tin  foil  one  millimeter  apart, 

without    an    intervening   dielectric. 

The  air  enters  the  space  between  the  plates  at  the  top  and 
sides,  and  is  sucked  down  through  the  opening  at  the  bottom 
of  the  ozonizer  by  the  action  of  the  water  at  B.  The  water 
carries  the  ozone  to  .A,  where  mixture  and  sterilization  take 
place.  The  current  in  the  transformer  is  of  course  turned  on 
only  when  water  is  drawn. 

5  Electrochem.  and  Met.  Ind.  6,  304,  (1908> 


APPENDIX 


TABLE  OF  ATOMIC  WEIGHTS 

O  =  16.00 


(1910)1 

(1910) 

Aluminum*     •     • 

.    .  Al 

27  1 

Helium     ... 

.     .  He 

4  0 

Antimony       •     • 

Sb 

120  2 

Hydrogen      •     • 

.    .  H 

1  008 

.   ".  A 

39.9 

.     .  In 

114.8 

.    .  As 

74.96 

.     .  I 

126.92 

.     .  Ba 

137.37 

.     .  Ir 

193  1 

Bismuth.     .     .     . 

.     .  Bi 

208  0 

.     .  Fe 

55  85 

Boron     .... 

.     .  B 

11  0 

Krypton   ... 

.     .  Kr 

83  0 

Bromine     •     .     . 

.     .  Br 

79  92 

Lanthanum  .     . 

.     .  La 

139  0 

Cadmium        . 

Cd 

112  40 

Lead                   • 

.     .  Pb 

207  10 

.     .  Cs 

132  81 

.     .  Li 

7.00 

Calcium 

.    .  Ca 

40  09 

.     .  Lu 

174  0 

Carbon  .... 

.    .  C 

12  00 

Magnesium  .     . 

.  Mg 

24  32 

C6rium  .... 

.     .  Ce 

140  25 

Manganese    .     . 

jAtg 
.    .  Mn 

54  93 

ChlorinB     ... 

Cl 

35  46 

M^ercury  .     .     * 

.  Hg 

200  0 

.    .  Cr 

52.0 

Molybdenum 

.     .  Mo 

96.0 

Cobalt    .... 

.    .  Co 

58.97 

Neodymium  .     . 

.     .  Nd 

144.3 

Columbium 

.    .  Cb 

93.5 

.    .  Ne 

20. 

Copper  .... 

.     .  Cu 

63.57 

Nickel.     .     .     . 

.    .  Ni 

58  68 

Dysprosium    .     . 

Dy 

162  5 

.    .  N 

14  01 

Erbium 

•  *-v 

.     .  Er 

167  4 

.    .  Os 

190  9 

Europiu  m 

.  Eu 

152  0 

.    .  O 

16  00 

.    .  Fl 

19.0 

Palladium     . 

.    .  Pd 

106.7 

Gadolinium    .     . 
Gallium 

.    .  Gd 
Ga 

157.3 
69  9 

Phosphorus  .     . 
Platinum      *     . 

.    .  P 

.    .  Pt 

31.0 

195  0 

Germanium    .     . 
Glucinum  . 

.     .  Ge 
.    .  Gl 

72.5 
9  1 

Potassium     .     . 
Praseodymium  . 

.    .  K 
.    .  Pr 

39.10 
140.6 

Gold  

.     .  Au 

197  2 

.     .  Rd 

226.4 

1  International  Committee  on  Atomic  Weights,  J.  Am.  Chem.  Soc.  32,  3,  (1910). 

315 


316 


APPENDIX 
TABLE  OF  ATOMIC  WEIGHTS  —  Continued 


(1910) 

(1910) 

Rhodium.    , 

.     .     .     .  Rh 

102.9 

Thallium  . 

.     .     .     .  Tl 

204.0 

Rubidium 

.    .    .     .  Rb 

85.45 

Thorium  . 

.     .     .     .  Th 

232  42 

Ruthenium 

Ru 

101.7 

Thulium  . 

....  Tm 

168  5 

.     .     .     .  Sm 

150.4 

Tin  .     .     . 

.     .     .     .  Sn 

119.0 

Scandium  • 

.    .    .    .  Sc 

44.1 

Titanium 

.    .     .     .  Ti 

48.1 

.    .    .    .  Se 

79.2 

Tungsten  . 

.     .     .     .  W 

184  0 

....  Si 

28  3 

Uranium 

...       U 

238  5 

Silver     .     . 

.  Atr 

107  88 

Vanadium 

y 

51  2 

.    .    .    .  Na, 

23.00 

.     .     .     .  Xe 

130.7 

.     .     .     .  Sr 

87.62 

Ytterbium 

.     .    .     .  Yb 

172.0 

Sulphur      • 

.    .    .    .  S 

32  07 

Yttrium    . 

.     .     .     .  Y 

89  0 

Tantalum 

.    .    .    .  Ta 

181  0 

Zinc     . 

Zn 

65  37 

Tellurium  . 

.    .    .    .  Te 

127.5 

Zirconium 

.     .     .     .  Zr 

90.6 

Terbium     . 

.    .    .    .  Tb 

159.2 

TABLE  OF  ELECTROCHEMICAL  EQUIVALENTS  OF  THE  MORE 
IMPORTANT  ELEMENTS1 


VALENCE 

MILLIGRAMS 
DEPOSITED  BY  1 
AMPERE  IN  1  SECOND 

GRAMS  DEPOSITED 
BY  1  AMPERE  IN 
1  HOUR 

.    .    .  Al 

3 

0.0935 

0.3366 

.    .    .  Sb 

3 

0.4152 

1.495 

...  As 

3 

0.2589 

0.9319 

.    .    .  Ba 

2 

0.7115 

0.1976 

.    .    .  Bi 

4 

0.5387 

1.939 

.    .    .  Br 

1 

0.8279 

2.981 

.     .    .  Cd 

2 

0.5821 

2.095 

.    .     .  Ca 

2 

0.2077 

0.7476 

.     .     .  Ce 

3 

0.4843 

1.744 

.    .    .  Cl 

1 

0.3673 

1322 

.     .    .  Cr 

2 

0.2694 

0.9696 

f| 

Cobalt     .... 

« 
...  Co 

3 

2 

0.1795 
0.3054 

0.6462 
1.099 

« 
Copper    .... 

« 
.    .    .  Cu 

3 
1 

0.2036 
0.6586 

0.7331 
2371 

1  Based  on  the  atomic  weights  of  1910  and  on  the  value  96,540  for  the  electro- 
chemical constant. 


APPENDIX 


317 


TABLE  OF  ELECTROCHEMICAL  EQUIVALENTS  —  Continued 


VALENCE 


MILLIGRAMS 

DEPOSITED  BY  1 

AMPERE  IN  1  SECOND 


GRAMS  DEPOSITED 

BY  1  AMPERE  IN 

1  HOUR 


Copper Cu  2 

Fluorine Fl  1 

Gold Au  1 

"  "  3 

Hydrogen H  1 

Iodine I  1 

Iron Fe  2 

"  «  3 

Lead Pb  2 

Lithium Li  1 

Magnesium  .  .  .  .  .  Mg  2 

Manganese Mn  2 

"  "  3 

Mercury Hg  1 

Nickel Ni  2 

"  «  3 

Oxygen O  2 

Potassium K  1 

Silver Ag  1 

Sodium Na  1 

Tin Sn  4 

Titanium Ti  4 

Zinc  .  .  Zn  2 


0.3293 

0.1968 

2.043 

0.6810 

0.01043 

1.313 

0.2894 

0.1929 

1.073 

0.0725 

0.1260 

0.2845 

0.1897 

2.071 

0.3039 

0.2026 

0.08287 

0.4051 

1.118 

0.2382 

0.3082 

0.1251 

0.3386 


1.186 

0.7086 

7.353 

2.451 

0.03758 

4.733 

1.042 

0.6947 

3.863 

0.261 

0.4534 

1.024 

0.6827 

7.457 

1.095 

0.7290 

0.2984 

1.458 

4.025 

0.8576 

1.109 

0.4504 

1.219 


NUMERICAL  RELATION  BETWEEN  VARIOUS  UNITS 

ENGLISH  AND  METRIC  MEASURES 

NOTE.— Values  taken  from  "Tables  of  Weights  and  Measures,"  U.  S.  Coast 
and  Geodetic  Survey,  1890. 

LENGTH 

1  meter  =  39.37  inches  (legalized  ratio  for  the  U.  S.) 

1  meter  =  1.093611  yard 

1  meter  =  3.280833  feet 

1  kilometer  =  0.621370  mile 

1  inch  =  25.40005  millimeters 

1  foot  =  0.304801  meter 


318  APPENDIX 

1  yard  =  0.914402  meter 
1  mile  =  1.609347  kilometer 

MASS 

1  kilogram  =  2.204622  pounds  av. 
1  grain  =  15.43235639  grains 
1  pound  =0.4535924277  kilograms 
1  ounce  av.  =  28.34853  grams 
1  ounce  troy  =  31.10348  grams 
1  metric  ton  =  1000  kilograms 

VOLUME 

1  liter  =  1.05668  quarts 
1  liter  =  0.26417  U.  S.  gallon 
1  liter  =  33.814  U.  S.  fluid  ounces 
1  quart,  U.  S.  =  0.94636  liter 
1  gallon,  U.  S.  =  3.78544  liters 
1  fluid  ounce  =  0.029573  liter 

MECHANICAL  EQUIVALENT  OF  HEAT 

1  kilogram-calorie  (1  kilogram  water  raised  1°  C.  at  15°  C.)  =  427.3 
kilogrammeters  (at  sea  level,  latitude  45°,  g  =  980.6  c.g.s.) 

1  British  thermal  unit  (1  pound  of  water  raised  1°  F.  at  59°  F.)  =  778.8 
foot  pounds  at  sea  level,  latitude  45° 

1  gram-calorie  (1  gm.  of  water  raised  1°  C.  at  15°  C.)= 4.190  x  107  ergs 

1  joule  =  107  ergs 

=  0.2387  gram-calorie 

ENERGY 

[Winkelmann,  Handbuch  der  Physik,  1,  79,  (1908)] 
1  kilowatt  =  1000  watts 

1  horse  power  (HP)  =     550  foot  pounds  per  second 
=     746  watts 
=  0.746  kilowatt 
1  kilowatt  =  1.34  horse  power 

The  metric  horse  power,  called  in  German  Pferdekraft  or  Pferde- 
stdrke  (PS) 

=  75  kilogrammeters  per  second 
=  736  watts 
Therefore  1  English  horse  power  =  1.014  metric  horse  power. 


APPENDIX  319 


LEGAL  ELECTRICAL  UNITS1 

The  legal  electrical  units  in  the  United  States  are  defined  as 
follows : 

(1)  The  unit  of  resistance  is  the  international  ohm,  represented 
by  the  resistance  offered  to  a  steady  current  by  a  column  of  mercury 
at  0°  C.  whose  mass  is  0.4521  gram,  of  a  constant  cross  section,  and 
whose  length  is  106.3  centimeters. 

(2)  The  unit  of  current  is  the  international  ampere  and  is  the 
equivalent  of  the  unvarying  current,  which,  when  passed  through 
a  solution  of  silver  nitrate  in  water,  in  accordance  with  standard 
specifications,  deposits   silver   at  the   rate   of  0.001118   gram  per 
second. 

The  specifications  for  the  practical  application  of  this  definition 
are  the  following: 

In  employing  the  silver  voltameter  to  measure  currents  of  about 
1  ampere,  the  following  arrangements  shall  be  adopted : 

The  cathode  on  which  the  silver  is  to  be  deposited  shall  take  the 
form  of  a  platinum  bowl  not  less  than  10  centimeters  in  diameter 
and  from  4  to  5  centimeters  in  depth. 

The  anode  shall  be  a  disk  or  plate  of  pure  silver  some  30  square 
centimeters  in  area  and  2  or  3  millimeters  in  thickness. 

This  shall  be  supported  horizontally  in  the  liquid  near  the  top  of 
the  solution  by  a  silver  rod  riveted  through  its  center.  To  prevent 
the  disintegrated  silver  which  is  formed  on  the  anode  from  falling 
upon  the  cathode,  the  anode  shall  be  wrapped  around  with  pure  filter 
paper,  secured  at  the  back  by  suitable  folding. 

The  liquid  shall  consist  of  a  neutral  solution  of  pure  silver  nitrate, 
containing  about  15  parts  by  weight  of  the  nitrate  to  85  parts  of 
water. 

The  resistance  of  the  voltameter  changes  somewhat  as  the  current 
passes.  To  prevent  these  changes  having  too  great  an  effect  on  the 
current,  some  resistance  besides  that  of  the  voltameter  should  be 
inserted  in  the  circuit.  The  total  metallic  resistance  of  the  circuit 
should  not  be  less  than  10  ohms. 

Method  of  Making  a  Measurement.  —  The  platinum  bowl  is  to  be 
washed  consecutively  with  nitric  acid,  distilled  water,  and  absolute 

1  Bulletin  of  U.  S.  Coast  and  Geodetic  Survey,  Dec.  27,  1893. 


320  APPENDIX 

alcohol ;  it  is  then  to  be  dried  at  160°  C.,  and  left  to  cool  in  a  desic- 
cator. When  thoroughly  cool  it  is  to  be  weighed  carefully. 

It  is  to  be  nearly  filled  with  the  solution  and  connected  to  the  rest 
of  the  circuit  by  being  placed  on  a  clean  insulated  copper  support  to 
which  a  binding  screw  is  attached. 

The  anode  is  then  to  be  immersed  in  the  solution  so  as  to  be  well 
covered  by  it  and  supported  in  that  position ;  the  connections  to  the 
rest  of  the  circuit  are  then  to  be  made. 

Contact  is  to  be  made  at  the  key,  noting  the  time.  The  current  is 
to  be  allowed  to  pass  for  not  less  than  half  an  hour,  and  the  time  of 
breaking  contact  observed. 

The  solution  is  now  to  be  removed  from  the  bowl  and  the  deposit 
washed  with  distilled  water  and  left  to  soak  for  at  least  six  hours. 
It  is  then  to  be  rinsed  successively  with  distilled  water  and  absolute 
alcohol  and  dried  in  a  hot-air  bath  at  a  temperature  of  about  160°  C. 
After  cooling  in  a  desiccator  it  is  to  be  weighed  again.  The  gain  in 
mass  gives  the  silver  deposited. 

To  find  the  time  average  of  the  current  in  amperes,  this  mass, 
expressed  in  grams,  must  be  divided  by  the  number  of  seconds 
during  which  the  current  has  passed  and  by  0.001118. 

In  determining  the  constant  of  an  instrument  by  this  method  the 
current  should  be  kept  as  nearly  uniform  as  possible  and  the  readings  of 
the  instrument  observed  at  frequent  intervals  of  time.  These  obser- 
vations give  a  curve  from  which  the  reading  corresponding  to  the  mean 
current  (time  average  of  the  current)  can  be  found.  The  current,  as 
calculated  from  the  voltameter  results,  corresponds  to  this  reading. 

The  current  used  in  this  experiment  must  be  obtained  from  a  bat- 
tery and  not  from  a  dynamo,  especially  when  the  instrument  to  be 
calibrated  is  an  electrodynamometer. 

(3)  The  unit  of   electromotive   force    is   the    international  volt, 
which  is  the  electromotive  force  that,  steadily  applied  to  a  conductor 
whose  resistance  is  one  international  ohm,  will  produce  a  current  of 
an  international  ampere,  and  is  practically  equivalent  to  ^—  of  the 
electromotive  force  of  a  Clark  cell,  at  15°  C.,  when  prepared  accord- 
ing to  the  standard  specifications.1 

(4)  The  unit  of  quantity  is  the  international  coulomb,  which  is 
the  quantity  of  electricity  transferred  by  a  current  of  one  interna- 
tional ampere  in  one  second. 

1  See  Bulletin  of  U.  S.  Coast  and  Geodetic  Survey,  Dec.  27,  1893. 


APPENDIX  321 

(5)  The  unit  of  work  is  the  joule,  equal  to  106  (see  under  Mech. 
Equiv.  of  Heat)  ergs,  and  is  practically  equivalent  to  the  energy 
expended  in  one  second  by  an  international  ampere  in  an  inter- 
national ohm. 

(6)  The  unit  of  power  is  the  watt,  and  is  practically  equivalent 
to  the  work  done  at  the  rate  of  one  joule  per  second. 


NAME   INDEX 


ABRAHAM  and  Marmier,  313. 

Acheson,  210,  217,  219,  220,  221. 

Adams,  34. 

Addicks,  47,  48,  53,  54. 

Adolph,  104,  105. 

Alexander,  203. 

Ashcroft,  234. 

Askenasy,  229. 

Baekeland,  130. 

Bancroft,  54. 

Becker,  234. 

Behr,  22. 

Behrend,  17. 

Bennie,  252. 

Berthelot,  220. 

Berzelius,  236. 

Betts,  64,  236. 

Bindschedler,  76. 

Birkeland,  279,  282,  287. 

Bjerrum,  15. 

Blount,  208. 

Bodenstein  and  Katayama,  275. 

Bodlander,  15. 

Boiling,  216. 

Borchers,  57,  75. 

Bottger,  19. 

Bradley,  230,  276. 

Braemer,  289. 

Bredig,  11,  266,  267. 

Brown,  55. 

Brush,  153. 

Bugarsky,  15. 

Bunsen,  6,  143,  228,  236. 

Burgess,  36,  146. 

Cantoni,  107. 
Caro,  266. 
Castner,  131,  233. 
Cavendish,  270. 
Coehn,  73. 
Cohen,  43. 
Colby,  259. 
Collins,  2. 

Colson,  209,  217,  218. 
Conrad,  207. 
Corbin,  125. 
Cowles,  185,  209,  229. 


Cowper-Coles,  41. 
Crocker,  126. 
Cruickshank,  21. 
Gumming,  15. 

Daniell,  143. 

Davy,  E.,  202. 

Davy,  H.,  228,  233,  236. 

Despretz,  208,  220. 

Deville,  228. 

Dietzel,  57. 

Dolezalek,  154. 

Donath  and  Frenzel,  276. 

Dony-Henault,  78. 

Easter  brooks,  51. 

Edison,  173,  182. 

Edstrom,  265. 

Elbs,  7,  77,  171. 

Elmore,  40. 

Endruweit,  41. 

Engelhardt,  117,  118,  122,  141. 

Erdmann,  16. 

Erlwein,  64,  266,  268. 

Eschmann,  267. 

Ewell,  311. 

Eyde,  281,  282. 

Faraday,  1. 

Farup,  4. 

Faure,  153. 

Ferranti,  259. 

Finckh,  271,  272. 

Fischer,  A.,  21,  25,  27,  29. 

Fischer,  F.,  289,  291. 

FitzGerald,  192,  200,  209,  211,  219,  220, 

224,  262. 
Fodor,  150. 
Foerster,  6,  24,  37,  45,  50,  55,  62,  67,  72, 

78,  79,  81,  82,  85,  88,  91-95,  97,  98, 

101-103,  109,  110,  112,  115,  116,  178, 

181,  183,  266. 
Fraenkel,  267. 
Frank,  266,  268,  287. 
Frazier,  216. 
Fromm,  45,  46. 

Gall  and  Montlaur,  123. 
Garuti  and  Pompili,  140. 
323 


324 


INDEX 


Gay-Lussac,  83. 
Gibbs,  Walcott,  21,  22. 
Gibbs,  W.  T.,  123. 
Girod,  257. 
Gladstone,  157,  158. 
Glaser,  106. 

Goodwin,  H.  M.,  14,  23. 
Goodwin,  J.  H.,  237. 
Gray,  310. 
Gronwall,  250. 
Grove,  143. 
Giinther,  45,  67. 
Guthrie,  11. 
Guthe,  1. 
Gyr,  115,  116. 

Haanel,  242. 

Haas,  120,  122. 

Haber,  36,  38,  55,  74,  206,  225,  271,  273, 

278,  285,  287. 
Haeussermann,  131. 
Hahn,  11. 
Hall,  229. 
Hambuechen,  146. 
Hamilton,  51. 
Hansen,  199. 

Hargreaves  and  Bird,  126. 
Hasse,  46,  67. 
Heim,  158. 
Heimrod,  2,  3. 
Hering,  187,  192,  198,  261. 
Hermite,  117. 
Herold,  181. 

Heroult,  230,  247,  249,  256. 
Herz,  77. 
Hessberger,  282. 
Hibbard,  252. 
Hoepfner,  44,  47. 
Hofman,  49. 
Holborn,  15. 
Holland,  173,  177. 
Holweg,  274. 
Horry,  206. 
Houston,  204. 
Howies,  276. 
Huber,  276. 
Hudson,  203. 
Hunt,  233. 
Hutton,  229. 

Isenburg,  76. 

Jablochkoff,  150. 
Jacobs,  227. 
Jacoby,  H.,  266. 
Jacoby,  M.  H.,  39. 
Jacques,  151. 
Jahn,  S.,  288,  290. 
Jakowkin,  80. 


Jellinek,  272. 
Job,  11. 
Joly,  J.,  11. 
Jorre,  82,  101;  103. 
Jost,  286. 

Keller,  254. 
Kellner,  118,  121. 
Kennelly,  173,  184,  204. 
Kennicutt,  204. 
Kershaw,  47,  123,  125,  243. 
Kiliani,  46,  49. 
Kistiakowsky,  11. 
Kjellin,  259,  262. 
Koenig,  273,  274. 
Kohlrausch,  F.,  8,  15. 
Kohlrausch,  W.,  158. 
Kretzschmar,  114. 

Lalande,  144. 

Lampen,  217. 

Langbein,  30,  35. 

Lebedeff,  229. 

Le  Blanc,  1,  22,  23,  25,  26,  69,  75,  76,  107, 

109,  159,  161,  267,  272. 
Le  Chatelier,  191. 
Leclanche,  143. 
Lederlin,  125. 
Ledingham,  6. 
Leithauser,  273,  292-311. 
Le  Rossignol,  286. 
Lewes,  202,  206,  207. 
Lewis,  15,  74. 
Liebenow,  161,  163. 
Lindblad,  249. 
Lombard,  267. 

Lorenz,  94,  109,  233. 
Lovejoy,  276. 
Luckow,  75. 
Luther,  81. 
Lyon,  251,  252. 

McDonald,  126. 

McDougall,  276. 

Magnus,  52,  54. 

Marchese,  43,  44. 

Marsden,  208. 

Marx,  289. 

Massenez,  291. 

Maynard,  59. 

Metzger,  153. 

Meves,  79. 

Moebius,  59. 

Moissan,  202,  209,  216,  220,  266. 

Monkton,  242. 

Miiller,  E.,  74,  81,  85,  89,  91-94,  97,  108- 

110,  112,  117. 
Muller,  F.  C.  G.,  10. 
Mylius,  45,  46. 


INDEX 


325 


Nahnsen,  46. 

Nernst,  1,  71,  74,  148,  271. 
Neumann,  232. 
Nicholson  and  Carlisle,  6. 
Northrup,  261. 
Niiranen,  272. 

Obach,  141. 
Oeschli,  99. 
Oersted,  228. 
Oettel,  4,  86,  92,  122. 
Olsen,  232. 
Ordway,  146. 
Osaka,  73. 
Ostwald,  13,  150. 
Otto,  314. 

Patterson,  131. 
Pauli,  115. 
Pauling,  283. 
Petavel,  229. 
Pinchon,  242. 
Plannhauser,  40. 
Plante,  152. 
Priestley,  270. 
Pyne,  231. 


Queneau,  191. 

Rathenau,  237. 

Rayleigh,  276. 

Readman,  227. 

Reichert,  16. 

Reinfeld,  41. 

Richards,  H.  C.,  195. 

Richards,  J.  W.,  123,  132,  204,  222,  277. 

Richards,  T.  W.,  1,  15,  22. 

Richardson,  131. 

Richarz,  7. 

Rochling  and  Rodenhauser,  262. 

Rostosky,  127. 

Russ,  310. 

Salom,  72. 
Salomon,  16. 
Sand,  81. 
Saunders,  41. 
Scheele,  220. 
Schmidt,  137. 
Schneider,  144. 
SchSnbein,  7. 
Schonherr,  282. 


Schoop,  141,  181. 

Schuckert,  119,  122. 

Schiitzenberger,  209,  217,  218. 

Seidel,  6. 

Senn,  65. 

Seward  and  von  Kugelgen,  238. 

Siemens,  243. 

Siemens  Brothers,  141. 

Siemens  and  Halske,  44,  312. 

Smith,  22. 

Soller,  74. 

Spitzer,  37. 

Sproesser,  96. 

Stadion,  99. 

Stalhane,  249. 

Stassano,  243,  254. 

Steiner,  105. 

Streintz,  160. 

Swan,  41. 

Tafel,  70. 

Taylor,  225. 

Thompson,  51,  202,  203,  232,  267. 

Tindal,  313. 

Tone,  219. 

Townsend,  129. 

Tribe,  157,  158. 

Tscheltzow,  160. 

Tucker,  203,  217,  220. 

Turnbull,  257. 

Ulke,  51,  54,  55. 
Uslar,  64. 

Varley,  146. 
Volta,  143. 

Walker,  117,  121. 

Warburg,  273,  290-311. 

Watson,  153. 

Wehrlin,  94. 

Whiting,  J.,  133. 

Whiting,  S.  E.,  173,  184. 

Wilke,  267. 

Willson,  202. 

Wilsmore,  14. 

Wohler,  F.,  202,  226,  228. 

Wohler,  P.,  237. 

Wohlwill,  50,  57,  58,  61,  112. 

Wologdine,  191. 

Zellner,  96. 


SUBJECT   INDEX 


Alkali  hydrate  and  chlorine ;  diaphragm 
process,  101-104;  bell  process,  104; 
mercury  cathode  process,  106 ;  mer- 
cury diaphragm  process,  107  ;  bell  cell, 
131 ;  Castner  cell,  135  ;  Hargreaves-Bird 
cell,  127  ;  McDonald  cell,  126  ;  Town- 
send  cell,  129;  Whiting  cell,  133-136. 

Aluminum,  first  isolated,  228  ;  reduction 
of  oxide  by  carbon,  229  ;  Hall's  process, 
229-230;  Bradley's  process,  230; 
Heroult's  process,  230 ;  furnace  for 
electrolytic  production,  231 ;  yield  per 
horse  power  day,  231 ;  temperature  of 
bath,  231 ;  table  of  production,  232 ; 
electrolytic  production  as  laboratory 
experiment,  232. 

Alundum,  227 ;  table  of  production,  228. 

Bell  alkali  chlorine  cell,  131. 
Brass  plating,  37. 
Bright  dipping  bath,  31. 
Bromate,  electrolytic  production  of,  115. 
Bromoform,   electrolytic  production   of, 
79. 

Calcium,  first  isolated,  236 ;  electrolytic 
production  by  Rathenau,  237 ;  by 
Seward  and  von  Kiigelgen,  238 ;  by  P. 
Wohler,  237. 

Calcium  carbide,  discovery,  202  ;  heat  of 
formation,  202 ;  equilibrium  with 
carbon  monoxide,  202 ;  chemical 
properties,  203 ;  Willson's  original 
furnace  for  manufacture  of,  204 ; 
first  furnace  at  Niagara  Falls,  205 ; 
Horry  furnace,  206  ;  yield  per  kilowatt 
day,  207 ;  raw  materials  for,  207 ; 
table  of  production,  206. 

Calcium  cyanamide,  discovery  of  produc- 
tion from  carbide,  266 ;  pressure  of 
nitrogen  in,  267 ;  chemical  behavior, 
268;  manufacture,  269. 

Carbon,  different  forms  distinguished, 
220. 

Carbon  bisulphide,  electrothermic  pro- 
duction; 225. 

Carbon    electrodes,    thermal    and    elec- 


trical conductivities  of,  198-199 ; 
porosity,  95-96 ;  as  anodes  in  alkali 
chloride  electrolysis,  95-97,  105. 

Carborundum,  first  produced,  208 ;  dis- 
covery by  Acheson,  210  ;  named,  210  ; 
furnace  at  Niagara  Falls  for  production 
of,  212 ;  reaction  of  formation,  212 ; 
raw  materials  for,  214 ;  yield  per  kilo- 
watt hour,  214 ;  table  of  production, 
215  ;  uses,  215  ;  analysis  of,  210,  216  ; 
temperature  of  formation  and  of  de- 
composition, 217 ;  chemical  properties, 
217. 

Carborundum  fire  sand,  211. 

Chlorate,  production  by  electrolytic  dis- 
charge of  hypochlorite,  85 ;  current  effi- 
ciency when  so  formed,  90 ;  electro- 
lytic production  in  acid  solution,  92 ; 
in  alkaline  solution,  84,  93 ;  current 
and  energy  yields,  98  ;  Gall  and  Mont- 
laur  cell  for  production  of,  123  ;  Gibbs 
cell,  123;  Lederlin  and  Corbin  cell, 
125. 

Chlorine,  chemical  action  on  hydrate, 
80-84 ;  electrolytic  production,  see 
Alkali  Hydrate. 

Chloroform,  electrolytic  production  of, 
79. 

Complex  salts  in  electroanalysis,  25,  28. 

Conductivity  measurement  as  method  of 
chemical  analysis,  15-16. 

Conductivity,  thermal ;  method  of  de- 
termining for  carbon  electrodes,  197 ; 
table  of  values  for  refractories,  191. 

Copper,  refining,  object  of,  47 ;  electro- 
lytic method,  48 ;  composition  of 
anodes,  48, 49  ;  composition  of  cathodes, 
49 ;  composition  of  slime,  50 ;  com- 
position of  fresh  electrolyte,  51 ;  of 
foul  electrolyte,  52 ;  behavior  of  im- 
purities in  anodes,  49 ;  circulation  of 
electrolyte,  52  ;  size  of  tanks,  52-54  ; 
multiple  and  series  systems  of  connec- 
tions, 53 ;  effect  of  temperature  on 
power  required,  54  ;  voltage  per  tank, 
54  ;  polarization,  54  ;  cost,  54. 

Copper,  winning  of,  43-45. 


327 


328 


INDEX 


Copper  plating,  35. 

Coulometers,  silver,  2-4 ;  copper,  4-6 
water,  6-11;  silver  titration,  11-12. 

Diaphragms,  construction  of,  75. 

Edison  storage  battery,  history  and  con- 
struction, 173-177  ;  table  of  different 
sizes,  177  ;  theory  of,  178-184 ;  nickel 
electrode,  composition  of,  178 ;  po- 
tential of,  179  ;  efficiency  of  charging 
181 ;  iron  electrode,  potential  of,  182 
effect  of  mercury  contained,  182 ; 
chemical  changes  in  battery,  183  ;  elec- 
tromotive force  of,  184 ;  capacity,  184  ; 
efficiency,  184. 

Electric  furnace,  classification,  186 ; 
design,  192,  199,  200;  heat  loss 
through  walls,  187 ;  through  elec- 
trodes, 193-198. 

Electrochemical  analysis,  by  potential 
measurement,  13-15 ;  by  conductiv- 
ity measurement,  15-16  ;  by  titration, 
with  a  galvanometer  as  indicator,  17- 
20;  by  electrolytic  deposition,  20- 
29 ;  change  in  potential  at  cathode 
during,  24. 

Electrochemical  equivalent,  1. 

Electrode  voltage,  196. 

Electrolytic  bleaching  solution,  see  Hy- 
pochlorite. 

Electromotive  series,  22. 

Electroplating,  30-34  ;  by  contact,  34 ; 
by  dipping,  34. 

Electrotyping,  39. 

Faraday's  laws,  1. 
Fluoride,  electrolysis  of,  113. 
Foil,  metallic,  electrolytic  production  of, 
41. 

Galvanometer  as  indicator  in  titrations, 
17-20. 

Galvanoplasty,  39. 

Gas  analysis  as  a  means  of  determining 
yield  of  hypochlorite,  86-87. 

Gold  plating,  38. 

Gold  refining,  61-64;  cyanide  process 
for  extracting  from  ore,  63. 

Graphite,  first  made  artificially,  220; 
theory  of  formation,  221 ;  furnace  for, 
222  ;  table  of  production,  224  ;  thermal 
and  electrical  conductivities  of,  198- 
199 ;  electrodes,  see  Carbon. 

Hydrogen,  electrolytic  production  of, 
137-141;  Schmidt  cell,  137;  Garuti 


and  Pompili  cell,  140 ;  Schoop  cell,  141 ; 
Siemens  Brothers  and  Obach  cell,  141. 

Hydrogen  electrode,  in  electroanalysis 
20. 

Hypobromite,  114. 

Hypochlorite,  production  by  action  of 
chlorine  on  hydrate,  80-84;  by  elec- 
trolysis of  alkali  chloride  solution  on 
smooth  platinum  electrodes,  84-94; 
effect  of  temperature,  88;  effect  of 
current  density,  89 ;  prevention  of  re- 
duction by  chromate,  89;  effect  of 
alkalinity  on  electrolytic  production, 
93 ;  effect  of  temperature  on  production 
in  alkaline  solution,  94  ;  decomposition 
point  of,  109  ;  production  with  platin- 
ized anode,  94 ;  with  carbon  anode, 
95  ;  effect  of  concentration  of  chloride 
solution  on  yield,  89,  96 ;  maximum 
concentration  attainable,  98 ;  current 
and  energy  yields,  98  ;  Hermite  cell  for 
electrolytic  production  of,  117;  Kell- 
ner  cell,  118,  121 ;  Haas  and  Oettel 
cell,  120,  122;  Schuckert  cell,  119, 
122. 

Hypoiodite,  115;  electrolytic  discharge 
of,  116. 

lodate,  115,  116. 

lodoform,  electrolytic  production  of,  77. 

Iron,  metallurgy  of,  239-242;  electro- 
thermic  reduction  from  ores,  242  ; 
Stassano's  preliminary  experiments  on, 
244;  Keller  furnace  for,  246;  He- 
roult's  experiments  on,  247-249 ;  fur- 
nace of  Gronwall,  Lindblad,  and  Stal- 
shane,  249 ;  furnace  at  H6roult,  Cali- 
fornia, 251. 

Lead  refining,  64-67. 

Mercury  cathode  in  electroanalysis,  22. 
Multiple  system  of  connections  in  metal 
refining,  53. 

Nickel  plating,  34. 

Nickel  refining,  55-57;  Orford  process, 
56. 

Nitrogen,  fixation  of ;  by  carbide,  266 ; 
pressure  of,  in  calcium  cyanamide,  267; 
yield  of  calcium  cyanamide  per  unit  of 
power,  269,  287 ;  by  oxidation  by  elec- 
tric discharge,  discovered,  270 ;  ther- 
mal equilibrium  in,  271 ;  electrical 
equilibrium,  274;  velocity  of  oxida- 
tion, 272  ;  yield  per  unit  of  power,  276, 
287 ;  apparatus  of  Bradley  and  Love- 
joy  for,  276,  277;  of  Birkeland  and 


INDEX 


329 


Eyde,  279-282  ;  of  Schonherr  and  Hess- 
berger,  282-283  ;  of  H.  and  G.  Pauling, 
283-285  ;   by  direct  union  with  hydro- 
gen, 285  ;  equilibrium,  286,  287. 
Nitrolime,  270. 

Overvoltage,  in  electroanalysis,  24 ;  in 
lead  storage  battery,  170  ;  in  reduction, 
71 ;  in  oxidation,  73. 

Oxidation,  electrolytic,  73 ;  catalytic 
effect  of  anode  on,  74 ;  of  chromium 
sulphate,  74 ;  of  attackable  anodes, 
75. 

Oxygen,  electrolytic  production  of,  see 
Hydrogen. 

Ozone,  discovery,  288  ;  heat  of  formation, 
288 ;  free  energy  of,  289 ;  velocity  of 
formation  by  silent  electric  discharge, 
290 ;  yields  by  different  methods  of 
production,  291 ;  maximum  concen- 
tration by  silent  discharge,  294-296 ; 
yield  per  coulomb,  for  negative  points, 
298-305  ;  effect  of  temperature,  302  ; 
of  pressure,  303 ;  of  concentration  of 
ozone  produced,  303  ;  of  water  vapor, 
303;  of  current  strength;  yield  per 
coulomb  for  positive  points,  305-308 ; 
effect  of  current  strength,  305 ;  of 
temperature,  305  ;  of  concentration  of 
ozone  produced,  305  ;  of  water  vapor, 
306 ;  yield  with  alternating  current, 
307  ;  yield  per  kilowatt  hour  for  posi- 
tive and  for  negative  points,  308 ; 
theory  of  formation,  309 ;  effect  of 
transparency  of  glass  ofozonizer,  310; 
ozonizer,  of  Siemens,  292,  309;  of  Sie- 
mens and  Halske,  312  ;  of  Tindal,  313  ; 
of  Abraham  and  Marmier,  313 ;  of 
Otto,  314. 

Parabolic  mirrors,  electrolytic  produc- 
tion of,  41. 

Perbromate,  115. 

Perchlorate,  chemical  formation,  84,  £ 
electrolytic  formation,   99 ;    technical 
cells  for,  126. 

Periodate,  117. 

Phosphorus,  226. 

Pinch  effect,  261. 

Potassium,  electrolytic  production  of,  see 
Sodium. 

Potential,  at  liquid-liquid  junctions,  elim- 
ination of,  15. 

Potential  measurement  as  method  oi 
analysis,  13. 

Primary  battery,  denned,  142 ;  Volta's 
Smee's,  Grove's,  Bunsen's,  chromic 
acid  cell,  Leclanche's,  143 ;  La- 


lande's,  144  ;  Daniell's,  145  ;  dry  cells, 
146  ;  Jacques's  cell,  151 ;  Jablochkoff  's 
cell,  150 ;  ideal  carbon  cell,  147 ;  free 
energy  of,  148. 

Quicking  bath,  38. 

deduction,  electrolytic;  denned,  68; 
reducing  power  of  cathode  measured 
by  its  potential,  69 ;  pressure  of  hy- 
drogen corresponding  to  different  po- 
tentials, 71 ;  catalytic  effect  of  cathode 
on,  72 ;  of  chromic  sulphate,  72 ;  of 
galena,  72. 

Secondary  battery,  defined,  142. 

Series  system  of  connection  in  metal 
refining,  53. 

Silicon,  electrothermic  production,  219. 

Siloxicon,  217-219. 

Silundum,  216. 

Silver  plating,  38. 

Silver  refining,  57  ;  Dietzel  process,  57 ; 
Moebius  process,  59. 

Sodium,  production  by  electrolysis  of 
fused  hydrate,  233;  Castner  cell  for, 
233 ;  Ashcroft  process,  234 ;  uses  of, 
236;  world's  production,  235. 

Steel,  electrothermic  refining  of,  252 ; 
Stassano's  furnace,  254 ;  Keller's, 
254;  Heroult's,  256;  Girod's,  257; 
Kjellin's,  259;  Rochling  and  Roden- 
hauser's,  262. 

Storage  battery  lead,  history  and  con- 
struction, 152-157  ;  chloride  cell,  154 ; 
Gould  cell,  156 ;  theory  of,  157-172  ; 
chemical  changes  in,  157 ;  change  in 
density  of  acid  on  charge  and  discharge, 
158 ;  electromotive  force,  160 ;  tem- 
perature coefficient,  161 ;  Le  Blanc's 
theory  of,  161 ;  Liebenow's  theory, 
163 ;  charge  and  discharge  curves, 
165-167;  capacity,  168;  current  effi- 
ciency, 169 ;  self-discharge,  169 ; 
sulphating,  171. 

Tubes,  electrolytic  production  of,  40. 
Voltameter,  see  Coulometer. 

White  lead,   electrolytic   production  of, 

77. 
Wire,  electrolytic  production  of,  40. 

Zinc,  electrolytic  winning  of,  45  ;  spongy, 

45,  46;    refining,  67. 
Zinc  plating,  33. 


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COMEY.  A  Dictionary  of  Chemical  Solubilities,  Inorganic.  By  ARTHUR  MES- 
SINGER  COMEY,  Ph.D.,  formerly  Professor  of  Chemistry,  Tufts  College. 

20  +  515  pages,  8vo,  d.,  $5.00  net 

FLEISCHER.  A  System  of  Volumetric  Analysis.  By  Dr.  EMIL  FLEISCHER. 
Translated,  with  Notes  and  Additions,  from  the  Second  German  Edition,  by 
M.  M.  Pattison  Muir,  F.R.S.E.,  Assistant  Lecturer  on  Chemistry,  The  Owens 
College,  Manchester. 

10  +  274  pages,  I2mo,  il.,  cL,  $2.00  net 

GATTERMANN.  The  Practical  Methods  of  Organic  Chemistry.  By  LUDWIG 
GATTERMANN,  Ph.D.,  Professor  in  the  University  of  Freiburg.  Authorized 
Translation  by  William  B.  Schober,  Ph.D.,  Instructor  in  Lehigh  University. 
Second  American  from  Fourth  German  Edition. 

J5  +  359  pages,  i2mo,  il.,  cL,  $1.60  net 


STANDARD  BOOKS  ON  CHEMISTRY  —  Continued 


LUPTON.  Chemical  Arithmetic.  With  Twelve  Hundred  Examples.  BY  SYDNEV 
LUPTON.  F.C.S. 

12  + 171  pages,  i6mo,  d.,  $1.10  net 

MENSCHUTKIN.  Analytical  Chemistry.  By  N.  MENSCHUTKIN,  Professor  in  the 
University  of  St.  Petersburg.  Translated  from  the  Third  German  Edition,  under 
the  Supervision  of  the  Author,  by  James  Locke. 

12+512  pages,  8vo,  cl.,  $4.00  net 

MEYER.  History  of  Chemistry  from  the  Earliest  Times  to  the  Present  Day. 
By  ERNEST  VON  MEYER,  Ph.D.  Translated  by  George  MacGowan,  Ph.D. 

8w,  cL,  $4.50  net 

MILLER.  The  Calculations  of  Analytical  Chemistry.  By  EDMUND  H.  MILLER, 
Ph.D.,  Professor  of  Analytical  Chemistry  in  Columbia  University.  Third 
Edition.  Revised  and  Enlarged. 

10  +  201  pages,  8vo,  cL,  $1.50  net 

MORGAN.  Qualitative  Analysis  as  a  Laboratory  Basis  for  the  Study  of  Gen- 
eral Inorganic  Chemistry.  By  WILLIAM  CONGER  MORGAN,  Ph.D.  (Yale), 
Assistant  Professor  of  Chemistry  in  the  University  of  California,  (c.) 

14  +  515  pages,  8vo,  il.,  cL,  $1.90  net 

NERNST.  Theoretical  Chemistry  from  the  Standpoint  of  Avogadro's  Rule  and 
Thermodynamics.  By  Professor  WALTER  NERNST,  Ph.D.,  of  the  University  of 
Gottingen.  Revised  by  the  Fourth  German  Edition. 

24  +  771  pages,  8vo,  cL,  $3.75  net 

NOYES.  Qualitative  Chemical  Analysis,  with  Explanatory  Notes.  By  ARTHUR 
A.  NOYES,  Ph.D.,  Professor  of  Theoretical  Chemistry  in  the  Massachusetts  Insti- 
tute of  Technology.  Third  Revised  and  Enlarged  Edition. 

89  pages,  8vo,  cl.,  $1.25  net 

OSTWALD.  The  Scientific  Foundations  of  Analytical  Chemistry  Treated  in 
an  Elementary  Manner.  Translated  by  George  MacGowan,  Ph.D. 

31  +  799  pages,  8vo,  cl.,  $2.00  net 

Manual  of  Physico-Chemical  Measurements.    Translated  by  James  Walker, 
D.Sc.,  Ph.D. 

12  +  255  pages,  il.,  cl.,  $2.25  net 

The  Principles  of  Inorganic  Chemistry.    Translated  with  the  Author's  Sanc- 
tion by  Alexander  Findlay,  M.A.,  B.Sc.,  Ph.D.     With  122  Figures  in  the  Text. 

27  +  785  pages,  8vo,  cl.,  $6.00  net 
All  by  WILHELM  OSTWALD,  Professor  of  Chemistry  in  the  University  of  Leipzig. 

REYCHLER.  Outlines  of  Physical  Chemistry.  By  A.  REYCHLER,  Professor  of 
Chemistry  in  the  University  of  Brussels.  Authorized  Translation  by  John 
McCrae,  F'h.D.  (Heid.).  With  52  Illustrations.  Second  Edition. 

16  +  268  pages,  cl.,  $1.00  net 


STANDARD  BOOKS  ON  CHEMISTRY  —  Continued 


HEMPEL.  Methods  of  Gas  Analysis.  By  Dr.  WALTHER  HEMPEL,  Professor  of 
Chemistry  in  Dresden  Technische  Hochschule.  Translated  from  the  Third 
German  Edition  and  Considerably  Enlarged  by  L.  M.  Dennis,  Professor  of 
Analytical  and  Inorganic  Chemistry  in  Cornell  University.  New  Edition. 

19  +  490  pages,  i2mo,  il.,  d.,  $2.25  net 

HERTER.  The  Common  Bacterial  Infections  of  the  Digestive  Tract,  and  the 
Intoxications  Arising  from  Them.  By  C.  A.  HERTER,  M.D.,  Professor  of 
Pharmacology  and  Therapeutics  in  Columbia  University,  Consulting  Physician 
to  the  City  Hospital,  New  York. 

x  +  360  pages,  index,  8w,  d.,  $1.50  net;  by  mail,  $1.62  net 

HILLYER.  Laboratory  Manual  :  Experiments  to  Illustrate  the  Elementary  Prin- 
ciples of  Chemistry.  By  H.  W.  HILLYER,  Ph.D.,  Assistant  Professor  of  Organic 
Chemistry  in  the  University  of  Wisconsin. 

6  +  198  pages,  8w,  d.,  90  cents  net 

JONES.     The  Theory  of  Electrolytic  Dissociation  and  Some  of  its  Applications. 

12  +  289  pages,  i2mo,  d.,  $1.60  net 

Elements  of  Physical  Chemistry. 

11  +565  pages,  8vo,  cL,  $4.00  net 

Elements  of  Inorganic  Chemistry. 

13  +  343  pages,  8vo,  d.,  $1.25  net 

Principles  of  Inorganic  Chemistry. 

20  +  521  pages,  $3.00  net 

All  by  HARRY  C.  JONES,  Professor  of  Physical  Chemistry  in  the  Johns  Hopkins 
University,  Baltimore. 

LASSAR-COHN.  A  Laboratory  Manual  of  Organic  Chemistry.  A  Compendium 
of  Laboratory  Methods  for  the  Use  of  Chemists,  Physicians,  and  Pharmacists. 
By  Dr.  LASSAR-COHN.  Translated  from  the  Second  German  Edition  by  Alex- 
ander Smith,  B.Sc.,  Ph.D. 

19  +  203  pages,  8vo,  d.,  $2.25  net 

LEBLANC.  The  Elements  of  Electro-Chemistry.  By  MAX  LEBLANC,  Professor 
of  Chemistry  in  the  University  of  Leipzig.  Translated  by  W.  R.  Whitney, 
Instructor  of  Chemistry  in  the  Massachusetts  Institute  of  Technology,  Boston. 
New  Edition,  revised  from  the  Third  German  Edition. 

10  +  282  pages,  I2md,  d.,  $1.50  net 

LENGFELD.  Inorganic  Chemical  Preparations.  By  FELIX  LENGFELD,  formerly 
Assistant  Professor  of  Inorganic  Chemistry  in  the  University  of  Chicago. 

9  +  55  PaSes)  I2mo,  d.,  60  cents  net 

LEWKOWITSCH.  Chemical  Technology  and  Analysis  of  Oils,  Fats,  and 
Waxes.  Third  Edition.  Entirely  Rewritten  and  Enlarged.  Eighty-eight 
Illustrations  and  Numerous  Tables.  Two  Volumes. 

16  +  12  + 1152  pages,  8vo,  il.,  d.,  $  12.00  net 

LEWKOWITSCH.  Laboratory  Companion  to  Fats  and  Oils  Industries.  By  Dr. 
J.  LEWKOWITSCH,  M.A.,  F.I.C.,  Examiner  in  Soap  Manufacture  and  in  Fats  and 
Oils  to  the  City  and  Guild  of  London  Institute. 

12  + 197  pages,  8w,  d.,  $ i.oo  net 


STANDARD  BOOKS  ON  CHEMISTRY—  Continued 


ROLFE.  The  Polariscope  in  the  Chemical  Laboratory.  An  Introduction  to 
Polarimetry  and  its  Application.  By  GEORGE  WILLIAM  ROLFE,  A.M.,  Instruc- 
tor in  Sugar  Analysis  in  the  Massachusetts  Institute  of  Technology. 

7+320  pages,  ismo,  il.,  d.,  $i.po  net 

ROSCOE  AND  SCHORLEMMER.  A  Treatise  on  Chemistry.  By  SIR  HENRY  E. 
ROSCOE  and  C.  SCHORLEMMER,  F.R.S.  Vol.1  —  The  Non-Metallic  Elements. 
New  Edition.  Completely  Revised  by  Sir  H.  Roscoe,  Assisted  by  Drs.  Colman 
and  Harden. 

12  +  931  pages,  8vo,  d.,  $5.00  net 

SCHNABEL.  Handbook  of  Metallurgy.  By  Dr.  CARL  SCHNABEL,  Konigl.  Preuss. 
Bergrath  Professor  of  Metallurgy.  Translated  by  Henry  Louis,  M.A.,  A.R.S.M., 
F.I.C.,  etc.,  Professor  of  Mining  at  Armstrong  College,  Newcastle-upon-Tyne. 
Second  Edition.  Vol.  I  —  Copper,  Lead,  Silver,  Gold.  Illustrated  with  715 
Figures,  (c.) 

20  + 1123  pages,  8vo,  U.,  cL,  $6.30  net 

SCHULTZ  AND  JULIUS.  A  Systematic  Survey  of  the  Organic  Colouring  Matters. 
Founded  on  the  German  of  Drs.  G.  SCHULTZ  and  P.  JULIUS.  Second  Edition. 
Revised  Throughout  and  Greatly  Enlarged  by  Arthur  G.  Green,  F.I.C.,  F.C.S. 

10  +  280  pages,  imperial  8vo,  d.,  $7.00  net 

SHERMAN.  Methods  of  Organic  Analysis.  By  HENRY  C.  SHERMAN,  Ph.D., 
Adjunct  Professor  of  Analytical  Chemistry  in  Columbia  University. 

245  pages,  8vo,  d.,  $1.75  net  (postage  140.} 

TALBOT.  An  Introductory  Course  of  Quantitative  Chemical  Analysis,  with 
Explanatory  Notes  and  Stoichiometrical  Problems.  By  HENRY  P.  TALBOT, 
Ph.D.,  Professor  of  Inorganic  and  Analytical  Chemistry  in  the  Massachusetts 
Institute  of  Technology. 

155  pages,  8vo,  d.,  $1.50  net 

TALBOT  AND  BLANCHARD.  The  Electrolytic  Dissociation  Theory.  With 
Some  of  its  Applications.  An  Elementary  Treatise  for  the  Use  of  Students  in 
Chemistry.  By  Professor  H.  P.  TALBOT  and  ARTHUR  A.  BLANCHARD,  both  of 
the  Massachusetts  Institute  of  Technology. 

4  +  84  pages,  8w,  cL,  $1.25  net 

THORP.  Outlines  of  Industrial  Chemistry.  A  Text-Book  for  Students.  By 
FRANK  HALL  THORP,  Ph.D.,  Assistant  Professor  of  Industrial  Chemistry  in  the 
Massachusetts  Institute  of  Technology.  Second  Edition.  Revised  and  En- 
larged, and  Including  a  Chapter  on  Metallurgy  by  Charles  D.  Demond,  S.B., 
Testing  Engineer  of  the  Anaconda  Mining  Company. 

26  +  618  pages,  8vo,  il.,  cl,  $3.75  net 

WALKER.  Introduction  to  Physical  Chemistry.  By  JAMES  WALKER,  D.Sc., 
Ph.D.,  F.R.S.,  Professor  of  Chemistry  in  University  College,  Dundee.  Fourth 
Edition. 

12  +  387  pages,  8vo,  d.,  $3.25  net 

VOUNG.  Fractional  Distillation.  By  SYDNEY  YOUNG,  D.Sc.,  F.R.S.  With  72 
Illustrations. 

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JAMES  WALKER'S 

Introduction  to  Physical  Chemistry 

Fourth  Edition,  8vo,  $3.25  net 

"  This  volume  by  Dr.  Walker  might  well  be  made  the  basis  of  a  course 
of  lectures,  intended  to  give  students  who  do  not  mean  to  specialize  in 
physical  chemistry  a  general  idea  of  the  subject,  while  the  same  course 
might  be  taken  with  profit  as  an  introductory  one  by  those  who  expect 
to  go  farther  in  the  subject.  The  author  has  been  very  successful 
along  the  lines  that  he  has  laid  down,  and  his  book  can  be  recom- 
mended heartily." — Journal  of  Physical  Chemistry. 

TABLE  OF  CONTENTS 

Units  and  Standards  of  Measurement  —  The  Atomic  Theory  and 
Atomic  Weights  —  Chemical  Equations  —  The  Simple  Gas  Laws  — 
Specific  Heats  —  The  Periodic  Law  —  Solubility  —  Fusion  and  Solidi- 
fication—  Vaporisation  and  Condensation  —  The  Kinetic  Theory  and 
Van  Der  Waal's  Equation  —  The  Phase  Rule  —  Thermochemical 
Change  —  Variation  of  Physical  Properties  in  Homologous  Series  — 
Relation  of  Physical  Properties  to  Composition  and  Constitution  — 
The  Properties  of  Dissolved  Substances  —  Osmotic  Pressure  and  the 
Gas  Laws  for  Dilute  Solutions  —  Deductions  from  the  Gas  Laws  for 
Dilute  Solutions  —  Methods  of  Molecular  Weight  Determination  — 
Molecular  Complexity  —  Dimensions  of  Atoms  and  Molecules  —  Elec- 
trolytes and  Electrolysis  —  Electrolytic  Dissociation  —  Balanced  Ac- 
tions —  Rate  of  Chemical  Transformation  —  Relative  Strength  of 
Acids  arid  of  Bases  —  Equilibrium  between  Electrolytes  —  Neutrality 
and  Salt  —  Hydrolysis  —  Applications  of  the  Dissociation  Theory  — 
Electromotive  Force  —  Thermodynamical  Proof — Index. 

WILLIAM  OSTWALD'S 
The  Scientific  Foundations  of  Analytical  Chemistry 

Cloth,  I2mo,  $2.00  net 
Translated  with  the  author's  sanction  by  George  M'Gowan. 

TABLE  OF  CONTENTS 

PART  I  —  THEORY.  The  Recognition  of  Different  Substances  —  The  Sepa- 
ration of  Substances  —  Physical  Methods  of  Separation  —  Chemical 
Separation  —  The  Quantitative  Determination  of  Substances. 

PART  II  —  APPLICATIONS.  Introduction  —  The  Hydrogen  and  Hydrox'yl  Ions 
—  The  Metals  of  the  Alkalies  — The  Metals  of  the  Alkaline  Earths  — 
The  Metals  of  the  Iron  Group  —  The  Metals  of  the  Copper  Group  — 
The  Metals  of  the  Tin  Group  —  The  Non  Metals  —  The  Calculation  of 
Analyses. 

APPENDIX  —  Lecture  Experiments. 


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HARRY  C.  JONES'S 

The  Elements  of  Physical  Chemistry 

Revised  Edition,  8vo,  $4.00  net 

*'  This  new  and  enlarged  edition  of  Professor  Jones's  well- 
known  text-book  will  be  welcomed  by  teachers  and  students 
of  physical  chemistry.  .  .  .  This  edition  has  been  exten- 
sively revised,  contains  a  large  amount  of  new  matter,  and 
is  a  satisfactory  realization  of  the  author's  aim,  as  stated  in 
the  preface,  to  bring  the  book  up  to  date.  The  volume  has 
been  increased  in  size  by  85  pages,  but  the  space  devoted 
to  new  material  is  somewhat  greater  than  this,  a  result  made 
possible  by  judicious  omissions.  Subjects  newly  or  more 
fully  treated  include  J.  J.  Thomson's  electron  theory ;  radio- 
activity;  the  work  of  Morse,  and  of  Lord  Berkeley  and 
E.  G.  J.  Hartley  on  the  direct  measurement  of  osmotic  pres- 
sure ;  colloidal  suspensions  ;  hydrolytic  dissociation  ;  conduc- 
tivity of  fused  salts ;  dissociation  in  non-aqueous  solvents ; 
catalysis ;  the  author's  hydrate  theory ;  researches  of  the 
author  and  co-workers  on  conductivity  and  viscosity  in  mixed 
solvents."  —  American  Chemical  Journal. 

"  The  brief,  but  carefully  prepared,  historical  sketches,  intro- 
ducing many  of  the  chapters,  as,  for  instance,  the  one  on 
'  Chemical  Dynamics  and  Equilibrium,'  and  the  great  num- 
ber of  references  to  original  papers  form  excellent  features 
of  the  book.  The  marked  enthusiasm  with  which  the  author 
writes  as  a  worker  in  the  field  is  bound  to  interest  the  stu- 
dent in  the  subject  as  a  living  one,  with  many  vital  problems 
yet  to  be  solved." — Journal  of  the  American  Chemical  Society. 


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LOUIS  KAHLENBERG'S 
Outlines  of  Chemistry 


Illustrated,  Cloth,  8w,  $2.60  net 


A  text-book  for  college  students  by  the  Professor  of  Chemistry 
and  Director  of  the  Course  in  Chemistry  in  the  University  of 
Wisconsin. 

"  The  first  five  chapters  are  mainly  devoted  to  experimental 
work  on  hydrogen,  oxygen,  and  chlorine  as  a  foundation  of 
fundamental  facts  and  laws  for  the  sixth  chapter  in  which  the 
atomic  and  molecular  theories  are  presented.  After  two  chap- 
ters devoted  to  ozone,  hydrogen  peroxide,  allotropy,  and  the 
halogens,  in  Chapter  IX,  acids,  bases,  and  salts,  hydrolysis, 
mass  action,  and  chemical  equilibrium  are  concisely  defined  on 
the  basis  of  facts.  Chapter  XVII  includes  the  elements  of 
thermochemistry ;  Chapter  XX,  classification  of  the  elements 
and  the  periodic  system,  and  Chapter  XXIV,  solutions,  elec- 
trolysis, and  electrochemical  theories.  In  this  arrangement  of 
the  essential  parts  of  chemical  theory,  and  with  this  mode  of 
treatment,  it  would  seem  that  the  author  has  kept  well  within 
the  limits  of  what  the  average  college  student  can  readily  com- 
prehend and  assimilate.  As  stated  in  the  preface,  the  student 
becomes  a  clear  logical  thinker  and  he  does  not  look  upon  the 
atomic  and  molecular  theories  as  something  arbitrary,  meta- 
physical, and  well-nigh  incomprehensible  ;  it  is  also  mentioned 
that  in  principle  this  is  the  method  of  Bunsen  and  of  many 
other  successful  teachers  of  chemistry.  Historical  connections 
are  kept  sufficiently  in  view  by  frequent  allusions.  The  cuts 
are  clear  and  well  made  and  the  subject  matter  well  printed. 
...  A  critical  examination  of  this  work  gives  the  impression, 
I  think,  that  the  author  has  accomplished  his  purpose  and  that 
he  has  given  us  one  of  the  best  books  and  in  some  respects  the 
best  book  that  has  been  prepared  on  this  subject." — Journal 
of  the  American  Chemical  Society. 


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